Add set-carrier command to modem script, with error checking.

Pull in the modemmanagers() function along the way.
(adapted from the flimflam mm.sh)

BUG=chromium-os:15089
TEST="modem set-carrier 'Generic UMTS'"

Change-Id: Ib7bbe8d84aeb7801621c11a8854c32f246753f2a
Reviewed-on: http://gerrit.chromium.org/gerrit/3888
Tested-by: Nathan J. Williams <njw@chromium.org>
Reviewed-by: Jason Glasgow <jglasgow@chromium.org>
Reviewed-by: Eric Shienbrood <ers@chromium.org>
2 files changed