Fix ceilometer-acompute rejoin problems

The problem was in the screenrc file generated, where the
following command appeared:

sg libvirtd "ceilometer-agent-compute
                 --config-file /etc/ceilometer/ceilometer.conf"^M"

The final "^M" was not then parsed.

Change-Id: Ie6c5b1c9e3d196a3a9c343c2afb46435711c10f5
Closes-bug: #1311666
Merge "Fix ceilometer-acompute rejoin problems"