cellular: Add common test setup and verification

BUG=chromium:403152
TEST=Run network_3GSmokeTest and network_3GSmokeTest.pseudomodem

Change-Id: Idb02cb69bed896383ed6ec55d62e91130d975aba
Reviewed-on: https://chromium-review.googlesource.com/213747
Reviewed-by: Prathmesh Prabhu <pprabhu@chromium.org>
Commit-Queue: Thieu Le <thieule@chromium.org>
Tested-by: Thieu Le <thieule@chromium.org>
20 files changed