adb: Avoid waiting for emulator connections

This change exempts the emulator connections from
WaitableConnection.WaitForConnection(). This is because emulator
connections are a) more reliable and b) handled a bit differently than
normal TCP connections.

Bug: 78991667
Test: emulator -showkernel ; adb shell
Change-Id: I552946198889a82d6c265f45e8c3b38f6ac9d045