gdb_remote: Add ssh_port flag

Add --ssh_port flag which allows users to specify the port number
to use during ssh connections with the remote device. This also
fixes the bug that gdb_remote cannot be used to debug a VM started
on a non-default port because vm port is hard coded as 9222 in
gdb_remote.

BUG=brillo:799
TEST=Manual tests

Change-Id: I6373e1735f0b01651bd0a39a445bfc4dc1f27a4a
Reviewed-on: https://chromium-review.googlesource.com/265071
Trybot-Ready: Yiming Chen <yimingc@chromium.org>
Tested-by: Yiming Chen <yimingc@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Queue: Yiming Chen <yimingc@chromium.org>
1 file changed