edit inheritence tree api/network/security_groups

changed negative tests from "smoke" to "gate"

avoid running "father's" test cases in son
both positive and negative now derive from common TestCase without
"test_" methods

previous:
BaseNetworkTest
	SecGroupTest
		NegativeSecGroupTest

new tree:
BaseNetworkTest
	BaseSecGroupTest
		SecGroupTest
		NegativeSecGroupTest

Change-Id: Ia438b9d0c591c1c250443f6b6d069d41b6d71097
Merge "edit inheritence tree api/network/security_groups"