test_fixed_ips unsafe xml/json resource sharing

Test fixed ips might store json test case
 related variables on the base class in way, which might cause the
xml test cases to uses the json rest clients.

Depending on the execution order, it can lead to many type of anomalies.

Fixing bug 1226001

Change-Id: Ib4585931aafcddf009a5a8001d4e14ce14053fe6
Merge "test_fixed_ips unsafe xml/json resource sharing"