Tweak scp command, to prevent uploading repositoryDir as a subdir of $version.

If for some reason (e.g., a forced rebuild), Buildbot rebuilds the same hrev,
it was possible for the scp command to place the repositoryDir as a subdir
in $arch/$version/, instead of as $arch/version. This should ensure that the
contents of repositoryDir are placed in $arch/$version/.