Add filter support to stack API

Accepts multiple request params ATTR=VALUE to filter the listed
stacks.  Stacks will be matched against all whitelisted filters
passed in the request.  Whitelisted filters for stacks are NAME
and STATUS.

If the same ATTR is passed multiple times, stacks matching ANY of the
values will be returned.

blueprint: filter-stacks
Change-Id: Ic9421a827e99793448c23a841006fb8c03819030
Use all available headroom for autoscaling

Fixes bug 1254796

Previously, potential headroom for autoscaling group growth
or shrinkage would remain unused unless the adjustment exactly
hit the max or min size respectively.

Now, we truncate the adjustment to the upper or lower bound
in the case of an over-shoot.

Change-Id: I760be999039f7038dab77cb8b77a0f683ef56db3
Merge "Use all available headroom for autoscaling"
Merge "Add filter support to stack API"