Ensure combination alarms can be evaluated

Fixes bug 1237589

Previously the retrieval of state for the constituent alarms always
failed for combination alarms, due to an incorrect attribute of
ceilometerclient being used. As a result combination alarms could
never be successfully evaluated.

Now the correct pluralized attribute is used.

Change-Id: Id58a5d185854367e5a08011048774ab5aed93d4e
Set python-six minimum version

missing python-six minimum version from the requirements.txt
set the min version to 1.4.1

fixes bug: #1237205

Change-Id: I6b821e4500178f4ca50e05c4893c8bbaacfc238e
Merge "Set python-six minimum version"
Merge "Ensure combination alarms can be evaluated"