labtunnel: fixed .cros hostname suffix handling for wificell

BUG=None
TEST=Ran "labtunnel wificell crossk-chromeos15-row1-rack2-host6.cros"
and was able to successfully tunnel to the correct hostnames for
-router.cros and -pcap.cros.

Change-Id: Ia3dba419dabbb182aca0f56ad5fc227168268c0e
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/3587222
Commit-Queue: Jared Bennett <jaredbennett@google.com>
Reviewed-by: Katherine Threlkeld <kathrelkeld@chromium.org>
Tested-by: Jared Bennett <jaredbennett@google.com>
Auto-Submit: Jared Bennett <jaredbennett@google.com>
1 file changed