autotest: network_3GModemControl: add autoconnect and random commands

Randomly use commands either to the device, the technology or the
modem and do this for several iterations to look for additional bugs.

Add support for testing both autoconnect=True and autoconnect=False

BUG=None
TEST=run this test

Change-Id: I23feb2159acd486e56ce02a4e15c0fed615ebdbd
Reviewed-on: https://gerrit.chromium.org/gerrit/10836
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Commit-Ready: Jason Glasgow <jglasgow@chromium.org>
Reviewed-by: Jason Glasgow <jglasgow@chromium.org>
Tested-by: Jason Glasgow <jglasgow@chromium.org>
3 files changed