Add Emergency Call testing mode

If 'isTesting' is true, this request is for testing purpose,
and must not be sent to a real emergency service; otherwise it's
a real emergency call request.

Bug: 122840137
Test: Treehugger (VTS later)
Merged-in: I9607967b2a362f72e9d2bcda4ef25afaf0cc7f1d
Change-Id: I9607967b2a362f72e9d2bcda4ef25afaf0cc7f1d
(cherry picked from commit 527d6506)