scripts: Export RSYNC_RSH environment variable in deploy-package.sh.

Otherwise it wouldn't be in effect when using the
'--remote-ssh-identity' option of the script.

* scripts/deploy-packages.sh (fetch_qt_deb) <RSYNC_RSH>: Export.
(deploy) <RSYNC_RSH>: Likewise.

Change-Id: Ia738402a16dad4eed3557137c82a3cdb6bbdeeef