distbuild: Add test suite for distbuild-helper

This is mostly to check that the 'cancel entire subprocess tree' works
as expected. Revert that patch and the test fails.

There are also some tweaks included in this commit.

Change-Id: If297522e6589ebb3a07dac66a39eb243789e53aa

1 files changed, 14 insertions, 0 deletions

diff --git a/distbuild-helper b/distbuild-helper
index 1f648dd4..b1300fb0 100755
--- a/distbuild-helper
+++ b/distbuild-helper
@@ -32,6 +32,20 @@ import urlparse
 import distbuild
 
 
+'''distbuild-helper
+
+This program exists to run other programs, and to make HTTP requests. It
+is used both by the distbuild controller (`morph controller-daemon` process)
+and the distbuild workers (`morph worker-daemon` processes).
+
+It communicates via JSON messages. For workers, it connects on the same port
+that the controller process connects. The controller has a special
+controller-helper-port which it uses for communication with its
+distbuild-helper process.
+
+'''
+
+
 class HelperMachine(distbuild.StateMachine):
 
     def __init__(self, conn):