We cleaned up most usage of global and extension resource attribute
maps in neutron with I2586f0b11b107d7f57214a0d65bcf7c38a5f0ebb
This patch follows suit in vmware-nsx by cleaning up modification of
attribute maps in the tests and instead using the fixture in parent
class setup method.
Change-Id: Ia51af39ceacac26455f7f274f28eff598b9e1e19