Add button in "hidden" settings to flip "VoLTE Provisioned" flag

VoLTE Provisioned flag can be lost when new device image is flashed. Currently
there is no way to trigger Verizon provisioning update from device. This patch
adds button in hidden settings which allow to manually change value of the
flag.

Bug: 19038362
Change-Id: I23f13004dbcf9eaf711c66261696772b1d7bfd6e