Implement guestagent Configuration Manager

Facilitate code reuse by implementing a manager class
that could be used by all guestagents to manage their configuration
files and overrides.

ConfigurationManager is responsible for management of
datastore configuration.
Its base functionality includes reading and writing configuration files.
It is responsible for validating user inputs and requests.
When supplied an override strategy it allows the user to manage
configuration overrides as well.

ConfigurationOverrideStrategy handles configuration files.
The strategy provides functionality to enumerate, apply and remove
configuration overrides (revisions).

The patch set also includes functionality for reading and writing
files and implements codecs for serialization and
deserialization of common configuration formats. The implemented
codecs get reused in the existing configuration parsers.

Includes a couple of little fixes to the taskmanager that will
be required by other datastores.

- Do not validate value ranges if min/max is not specified in the
validation rules.
- Do not attempt to parse non-string configuration values in the
taskmanager.

Implements: blueprint guestagent-configuration-manager
Change-Id: I1c940c96deb20ca722d9fd400a6ef757b2ba249f

1 files changed, 22 insertions, 0 deletions

diff --git a/trove/common/utils.py b/trove/common/utils.py
index fc43cc01..77411094 100644
--- a/trove/common/utils.py
+++ b/trove/common/utils.py
@@ -14,11 +14,13 @@
 #    under the License.
 """I totally stole most of this from melange, thx guys!!!"""
 
+import collections
 import datetime
 import inspect
 import os
 import shutil
 import time
+import types
 import uuid
 
 from eventlet.timeout import Timeout
@@ -289,3 +291,23 @@ def gen_ports(portstr):
     if int(from_port) > int(to_port):
         raise ValueError
     return from_port, to_port
+
+
+def unpack_singleton(container):
+    """Unpack singleton collections.
+
+    Check whether a given collection is a singleton (has exactly one element)
+    and unpack it if that is the case.
+    Return the original collection otherwise.
+    """
+    if is_collection(container) and len(container) == 1:
+        return unpack_singleton(container[0])
+
+    return container
+
+
+def is_collection(item):
+    """Return True is a given item is an iterable collection, but not a string.
+    """
+    return (isinstance(item, collections.Iterable) and
+            not isinstance(item, types.StringTypes))