Fix instance object's use of a db query method parameter

The limit and marker arguments are kwargs, which need to be
correct to pass some mock tests in the unit tests for api.

Related to unified-object-model

Change-Id: I16b45ff73a6d79313fdd4a1124309f558497ab72
Make info_cache handle when network_info is None

The info_cache['network_info'] data can be None, so don't string-
convert it to 'None'.

Related to blueprint unified-object-model

Change-Id: I7a18f9189ab31beca0f8df764531387b4dd41b50
Merge "Fix instance object's use of a db query method parameter"
Merge "Make info_cache handle when network_info is None"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp