ctest: add ssh_port option

Add --ssh_port option to ctest to specify which port should
we used to access the image.

This option helps us to launch different VM used for VMTest so that we
can running them in parallel.

TEST=tryjob betty-vmtest-informational
TEST=manual run ctest

Change-Id: Id183da11f6eb9e2b5bc69477055b0119185552d3
Reviewed-on: https://chromium-review.googlesource.com/724276
Commit-Ready: Po-Hsien Wang <pwang@chromium.org>
Tested-by: Po-Hsien Wang <pwang@chromium.org>
Reviewed-by: Ilja H. Friedel <ihf@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
4 files changed