Fix CA cert tests

There were two issues with the current test:
1) Apps targeting N that want to trust the user added CA store must
opt-into it with a Network Security Config.
2) The test relied on TrustManagers seeing updates to the user CA store,
this isn't really the case (yet) so take advantage of a testApi to
inform the NetworkSecurityConfig of a trusted storage change.

Bug:27526668
Change-Id: If1d425746379fde86e8da8a70e27fa6254671066
4 files changed