lshal: add wait command

Waits for an interface to start (e.g. for scripting certain tests).

Fixes: 135956088
Test: the following
$ adb shell lshal wait android.hardware.nfc@1.0::INfc/foo
Service not found (missing permissions or not in VINTF manifest?).
$ echo $?
128
$ adb shell lshal wait android.hardware.nfc@1.0::INfc/default
$ echo $?
0
Test: lshal_test

Change-Id: I355fc33f9e46bac573a38425205e8db81f19a36e