Add test coverage for NetworkSpecifiers.

Tests various combinations of empty / non-empty NetworkSpecifiers
and changing specifiers on the fly.

Test: ConnectivityServiceTest passes
Bug: 27533960
Bug: 36053921
Change-Id: Ibd6b4efc861dc51689e46f3882ba859223411bf0
Merged-In: Ia7d36096f0e3f0b203d1d838043c03fcd1cea829
Merged-In: Ia71b72cc10dba6bac7c8fbe1ab3c5f40bc5506ff
1 file changed