MB-12536: Ignoring dirname error for CentOS 6.6 for couchbase-server start during installation

Change-Id: I409cfa27313ff0e9beb0aa060724a0e6865583ed
Reviewed-on: http://review.couchbase.org/42733
Reviewed-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>
Tested-by: Sangharsh Agarwal <sangharsh.agarwal@globallogic.com>