[CTS] Fix flakiness in profile B&R tests

1) Don't use wait-for-broadcast-idle to detect user started since other
unrelated broadcasts can fill the queue.
2) Wait for transport initialization before trying to switch transports.
3) Wait for user stopping to complete.

Bug: 122305663
Test: atest CtsBackupHostTestCases (with multiple iterations)
Change-Id: I2367b7cdb615c6274a9aedbb557778544bb3c5f8
2 files changed