Use the list when get information from libvirt

If the libvirt adds new elements to the domain info struct or others,
when use the new libvirt, there will be a valueError (too many values
to unpack). When we get information from libvirt, we should use the
original variable format. This change is for compatibility with upcoming
versions of libvirt which change this signature.

Change-Id: I885a48b730acd618e7cefc93cee3d69226575b7c
Closes-Bug: #1291805
Disable specifying alarm itself in combination rule

Currently, update combination alarm can specify itself in alarm_ids,
however, that will cause endless loop when evaluating this alarm.

This patch adds a check to disable such behavior.

Change-Id: I63b465c59fe39206ae04b0736482d1ffd7bf59c4
Closes-Bug: #1304419
Replace assert statements with assert methods

Some of the test methods were using python assert
statements for making assertions. This patch replaces
those statements with apropriate assert methods.

Change-Id: I3fcf4253560474868a0b32a7994f446e7b4bcc67
Closes-bug: #1303124
Merge "Replace assert statements with assert methods"
Fix a response header bug in the error middleware

Coerce the Content-Length of the custom error message to a string, not an
integer.  Some pure Python WSGI servers aren't strict and violate the WSGI
specification by automatically converting the value to a string.  Apache,
however, *is* strict, and considers this a 500 Internal Error

Fixes bug 1306963

Change-Id: I9b82ceee096b00c21c3b230dc67701bc40629968
Merge "Disable specifying alarm itself in combination rule"
Merge "Fix a response header bug in the error middleware"
Merge "Use the list when get information from libvirt"