Binding on-demand #9: selectBackupTransport[Async]

Migrate selectBackupTransport()/selectBackupTransportAsync() to binding
on-demand. To mimic the bind-if-needed behavior that existed before for
selectBackupTransportAsync we now register-if-needed in the selection.
This means a new registerTransport() method was created in the
TransportManager. I intend to use this method with only few
modifications for the first-binding code.

Change-Id: I39661cff0f7b2f8a27da37905dcd93e0aa9b1178
Ref: http://go/br-binding-on-demand
Bug: 17140907
Test: m -j RunFrameworksServicesRoboTest
Test: adb shell bmgr transport <transport>, observe logs
Test: Robolectric tests for TransportManager will go in registration CL