Added description of operators for extra_specs
Added description of operators for extra_specs

There are several new operators added for extra_specs that are used
in compute capability filter and aggregate filter. These are
described in document in this patch. Fixed bug 1047036.

Change-Id: Id86c6672d7bda458ecb918f1900d6f8a9526ad41

paulmathews/nova,NewpTone/stacklab-nova,paulmathews/nova,savi-dev/nova,paulmathews/nova,NewpTone/stacklab-nova,savi-dev/nova,NewpTone/stacklab-nova,savi-dev/nova