remote_access: Add some helper command for copying with rsync
remote_access: Add some helper command for copying with rsync

It's nice to be able to use rsync for copies (much faster).  Add a few
helper functions for doing this, handling fallback to just using tar
to send.

BUG=None
TEST=Use in a future CL

Change-Id: I74c481520fc785138875ab6d5ffdaf9935a0b6d1
Reviewed-on: https://gerrit.chromium.org/gerrit/39392
Tested-by: Doug Anderson <49983c4a76b998672954ed5edf4a62db4a336502@chromium.org>
Reviewed-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@chromium.org>
Reviewed-by: Mandeep Singh Baines <19acf4ef1f391f4aab404dc5703cac3632e06f3a@chromium.org>
Commit-Ready: Doug Anderson <49983c4a76b998672954ed5edf4a62db4a336502@chromium.org>

zhang0137/scripts,crawford/scripts,nicescale/scripts,sigma/coreos-scripts,fivethreeo/scripts,zhang0137/scripts,mischief/scripts,trnubo/scripts,gtank/scripts,bcwaldon/coreos-scripts,zhang0137/scripts,mjg59/scripts,mischief/scripts,coreos/scripts,bcwaldon/coreos-scripts,glevand/coreos--scripts,endocode/scripts,mjg59/scripts,marineam/coreos-scripts,vmware/coreos-scripts,endocode/scripts,BugRoger/scripts,andrejro/coreos--scripts,sigma/coreos-scripts,fivethreeo/scripts,crawford/scripts,smilart/scripts,sigma/coreos-scripts,mjg59/scripts,endocode/scripts,mischief/scripts,nicescale/scripts,vmware/coreos-scripts,BugRoger/scripts,gtank/scripts,andrejro/coreos--scripts,gtank/scripts,crawford/scripts,marineam/coreos-scripts,smilart/scripts,coreos/scripts,marineam/coreos-scripts,smilart/scripts,vmware/coreos-scripts,trnubo/scripts,trnubo/scripts,nicescale/scripts,bcwaldon/coreos-scripts,BugRoger/scripts,glevand/coreos--scripts,andrejro/coreos--scripts,fivethreeo/scripts