Force ceph.conf file mode to 0644

This configuration file doesn't include any credential even with cephx
authentication. It also prevents running ceph commands as a non-root user which
has access to appropriate keyring file.
Fix test with default ceph.conf mode

Change-Id: I7620a31e0e174eed002202d2c6873feb6884ed6c
Merge pull request #34 from ctrlaltdel/ceph-conf-mode

Force ceph.conf file mode to 0644