More unittests for quantum.api.v2.base

Added unittests for the below methods
* quantum.api.v2.base._fields()
* quantum.api.v2.base._filters()
* quantum.api.v2.base.create_resource()

Fixes bug #1092399

Change-Id: Icdddb3a201b4bc577378e78c7a7cd48486a2d57a
Merge "More unittests for quantum.api.v2.base"