Test TetheringManager could be GC after getting connector

There is pollingConnector thread which start polling connector if
TetheringManager is created earlier than TetheringService started(during
device boot up). TetheringManager won't be GCed if pollingConnector
thread do not finish its task yet.

Bug: 177265744
Bug: 191798390
Bug: 187972579
Test: atest TetheringServiceTest
Change-Id: Id8c7d10c5172e1d5de460c5311ff9c20261facef
1 file changed