Disable MDS and RGW from default

MDS and RGW are not deployed often (RGW more), so we disable them from
the default deployment to only get MONs and OSDs.

Signed-off-by: Sébastien Han <sebastien.han@enovance.com>
Merge pull request #156 from leseb/disable-default-mds-rgw

Disable MDS and RGW from default