WifiManagerTest: Re-enable testFactoryReset

The full factory reset test will cause the device to lose its saved
networks after the test app is uninstalled. There isn't a way to fix the
change of ownership for saved networks after the reset. So, add a
negative test instead.

Bug: 152637504
Test: atest WifiManagerTest#testFactoryReset
Change-Id: If5fa76cbfdc17d10da3340b7b65221fd8a0f5632
1 file changed