RunRemote was adding user@host: prefixes on top of the paths already
pre-prefixed by engine.go in the remote-to-remote branch, causing
"both remote" rsync errors. The source path was also incorrectly
prefixed with srcUserHost:, making rsync reject the command entirely.
The fix: buildArgs already orders args correctly for rsync (source
then dest), so just use args[-2] and args[-1] as-is without any
additional prefixing.
darroyo
5b28b46e6b