remote_access: ping the device before attempting to establish ssh connection
remote_access: ping the device before attempting to establish ssh connection

Users often pass the wrong IP address when using `cros
flash/deploy`. By adding the step of pinging the device first, we
avoid waiting for the long SSH connection timeout, which is required
to connect to the sometimes very slow VMs.

Note that if the remote device is pingable yet non-sshable
(i.e. perhaps not device you want to connect to), `cros flash/deploy`
will still wait until the SSH connection timeout expires.

BUG=chromium:383654
TEST=`cros flash invalidip latest`

Change-Id: Iccb2fbdae6fdad91fac63b4e5a111be6df56c1ed
Reviewed-on: https://chromium-review.googlesource.com/204686
Reviewed-by: Yu-Ju Hong <52dc720c411f8e2156e608c1a8b894a917489667@chromium.org>
Commit-Queue: Yu-Ju Hong <52dc720c411f8e2156e608c1a8b894a917489667@chromium.org>
Tested-by: Yu-Ju Hong <52dc720c411f8e2156e608c1a8b894a917489667@chromium.org>

chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,bpsinc-native/src_third_party_chromite