Set IMEI in provisioning helper

Borrow the code from AttestKeyTest.cpp (in KeyMint VTS) for determining
the devices IMEI value(s), and use that as default value.

Also update to use the newer provisioning message if the second IMEI is
set.

Test: provision a test device
Change-Id: Ie8e183dc50ac9107c2c2c2966c591e8b6022fd20