Fix adb flakiness on reboot

bug: 31950237

There are two lists of active ADB transports (devices),
and with the emulator, they can go out of sync.

This CL more conservatively checks if there are no
transports in either list before commiting to
register a new transport for the emulator.

Change-Id: Id1201dc59c70825881dad80925c2e5bcc13dbd5e
(cherry picked from commit edaedfd5)