[FIXED-JENKINS-12821] Use four-digit ports and 'emulator' identifier.

The Android emulator does not connect to ADB properly if used with a non 4-digit
port number.  See http://b.android.com/60024

Switching from the 'localhost' to 'emulator' style of identifier also fixes the
problem in JENKINS-22334, which started happening in recent SDK tools versions.