cts: actively request for location when run magnetic field tests

Instead of using getLastKnownLocation, use getCurrentLocation to
actively request for location. Otherwise, its very likely the tests
aren't getting any location at all.

Test: CtsVerifier: Magnetic Field Measurement Test
Bug: 319176581
Change-Id: I1da49d10f336afbb509d1f097d043f9790978d62
1 file changed