Fix flake in testMobileDataAlwaysOn

The internal structure backing getAllNetworks is updated after
invoking lost callbacks, so the test needs to wait for the handler
to be idle before calling getAllNetworks.

Also avoid assertions in finally clauses, as it causes confusing
error messages.

Bug: 185081944
Change-Id: I8ad5ab45a3e65b0031672e6f594b1a6d6ad5abcb
Test: atest ConnectivityServiceTest
1 file changed