Fix Ceph and Swift precheck failure

If enable Ceph MDS and RBD services, they are not conflicting
with Swift service.

Fix the check condition to make sure both Ceph and Swift exist.

Closes-Bug: #1747592

Change-Id: Icc6806125ce72992f7dff00c30d591ffb737a0c6
Signed-off-by: Tone.Zhang <tone.zhang@arm.com>