Allow non-interactive execution of install_server

This PR adds the ability to execute the installation script non-interactively, useful for automated provisioning scripts such as Chef, Puppet, Ansible, Salt, etc.
Simply feed the environment variables into the install script to skip the prompts.

For debug and verification purposes, the script will still output the selected config variables.
The plus side is that the environment variables also support command substitution (see REDIS_EXECUTABLE).

```
sudo REDIS_PORT=1234 REDIS_CONFIG_FILE=/etc/redis/1234.conf REDIS_LOG_FILE=/var/log/redis_1234.log REDIS_DATA_DIR=/var/lib/redis/1234 REDIS_EXECUTABLE=`command -v redis-server` ./utils/install_server.sh

Welcome to the redis service installer
This script will help you easily set up a running redis server

Selected config:
Port           : 1234
Config file    : /etc/redis/1234.conf
Log file       : /var/log/redis_1234.log
Data dir       : /var/lib/redis/1234
Executable     : /usr/local/bin/redis-server
Cli Executable : /usr/local/bin/redis-cli
Copied /tmp/1234.conf => /etc/init.d/redis_1234
Installing service...
Successfully added to chkconfig!
Successfully added to runlevels 345!
Starting Redis server...
Installation successful!
```

1 files changed, 45 insertions, 28 deletions

diff --git a/utils/install_server.sh b/utils/install_server.sh
index 98e047e3d..34c238197 100755
--- a/utils/install_server.sh
+++ b/utils/install_server.sh
@@ -42,6 +42,7 @@ SCRIPTPATH=$(dirname $SCRIPT)
 
 #Initial defaults
 _REDIS_PORT=6379
+_MANUAL_EXECUTION=false
 
 echo "Welcome to the redis service installer"
 echo "This script will help you easily set up a running redis server"
@@ -53,47 +54,61 @@ if [ "$(id -u)" -ne 0 ] ; then
 	exit 1
 fi
 
-#Read the redis port
-read  -p "Please select the redis port for this instance: [$_REDIS_PORT] " REDIS_PORT
 if ! echo $REDIS_PORT | egrep -q '^[0-9]+$' ; then
-	echo "Selecting default: $_REDIS_PORT"
-	REDIS_PORT=$_REDIS_PORT
+	_MANUAL_EXECUTION=true
+	#Read the redis port
+	read  -p "Please select the redis port for this instance: [$_REDIS_PORT] " REDIS_PORT
+	if ! echo $REDIS_PORT | egrep -q '^[0-9]+$' ; then
+		echo "Selecting default: $_REDIS_PORT"
+		REDIS_PORT=$_REDIS_PORT
+	fi
 fi
 
-#read the redis config file
-_REDIS_CONFIG_FILE="/etc/redis/$REDIS_PORT.conf"
-read -p "Please select the redis config file name [$_REDIS_CONFIG_FILE] " REDIS_CONFIG_FILE
 if [ -z "$REDIS_CONFIG_FILE" ] ; then
-	REDIS_CONFIG_FILE=$_REDIS_CONFIG_FILE
-	echo "Selected default - $REDIS_CONFIG_FILE"
+	_MANUAL_EXECUTION=true
+	#read the redis config file
+	_REDIS_CONFIG_FILE="/etc/redis/$REDIS_PORT.conf"
+	read -p "Please select the redis config file name [$_REDIS_CONFIG_FILE] " REDIS_CONFIG_FILE
+	if [ -z "$REDIS_CONFIG_FILE" ] ; then
+		REDIS_CONFIG_FILE=$_REDIS_CONFIG_FILE
+		echo "Selected default - $REDIS_CONFIG_FILE"
+	fi
 fi
 
-#read the redis log file path
-_REDIS_LOG_FILE="/var/log/redis_$REDIS_PORT.log"
-read -p "Please select the redis log file name [$_REDIS_LOG_FILE] " REDIS_LOG_FILE
 if [ -z "$REDIS_LOG_FILE" ] ; then
-	REDIS_LOG_FILE=$_REDIS_LOG_FILE
-	echo "Selected default - $REDIS_LOG_FILE"
+	_MANUAL_EXECUTION=true
+	#read the redis log file path
+	_REDIS_LOG_FILE="/var/log/redis_$REDIS_PORT.log"
+	read -p "Please select the redis log file name [$_REDIS_LOG_FILE] " REDIS_LOG_FILE
+	if [ -z "$REDIS_LOG_FILE" ] ; then
+		REDIS_LOG_FILE=$_REDIS_LOG_FILE
+		echo "Selected default - $REDIS_LOG_FILE"
+	fi
 fi
 
-
-#get the redis data directory
-_REDIS_DATA_DIR="/var/lib/redis/$REDIS_PORT"
-read -p "Please select the data directory for this instance [$_REDIS_DATA_DIR] " REDIS_DATA_DIR
 if [ -z "$REDIS_DATA_DIR" ] ; then
-	REDIS_DATA_DIR=$_REDIS_DATA_DIR
-	echo "Selected default - $REDIS_DATA_DIR"
+	_MANUAL_EXECUTION=true
+	#get the redis data directory
+	_REDIS_DATA_DIR="/var/lib/redis/$REDIS_PORT"
+	read -p "Please select the data directory for this instance [$_REDIS_DATA_DIR] " REDIS_DATA_DIR
+	if [ -z "$REDIS_DATA_DIR" ] ; then
+		REDIS_DATA_DIR=$_REDIS_DATA_DIR
+		echo "Selected default - $REDIS_DATA_DIR"
+	fi
 fi
 
-#get the redis executable path
-_REDIS_EXECUTABLE=`command -v redis-server`
-read -p "Please select the redis executable path [$_REDIS_EXECUTABLE] " REDIS_EXECUTABLE
 if [ ! -x "$REDIS_EXECUTABLE" ] ; then
-	REDIS_EXECUTABLE=$_REDIS_EXECUTABLE
-
+	_MANUAL_EXECUTION=true
+	#get the redis executable path
+	_REDIS_EXECUTABLE=`command -v redis-server`
+	read -p "Please select the redis executable path [$_REDIS_EXECUTABLE] " REDIS_EXECUTABLE
 	if [ ! -x "$REDIS_EXECUTABLE" ] ; then
-		echo "Mmmmm...  it seems like you don't have a redis executable. Did you run make install yet?"
-		exit 1
+		REDIS_EXECUTABLE=$_REDIS_EXECUTABLE
+
+		if [ ! -x "$REDIS_EXECUTABLE" ] ; then
+			echo "Mmmmm...  it seems like you don't have a redis executable. Did you run make install yet?"
+			exit 1
+		fi
 	fi
 fi
 
@@ -112,7 +127,9 @@ echo "Data dir       : $REDIS_DATA_DIR"
 echo "Executable     : $REDIS_EXECUTABLE"
 echo "Cli Executable : $CLI_EXEC"
 
-read -p "Is this ok? Then press ENTER to go on or Ctrl-C to abort." _UNUSED_
+if $_MANUAL_EXECUTION == true ; then
+	read -p "Is this ok? Then press ENTER to go on or Ctrl-C to abort." _UNUSED_
+fi
 
 mkdir -p `dirname "$REDIS_CONFIG_FILE"` || die "Could not create redis config directory"
 mkdir -p `dirname "$REDIS_LOG_FILE"` || die "Could not create redis log dir"