vstart.sh: rename conf variable to conf_fn

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
vstart.sh: echo CEPH_{CONF,KEYRING} exports if necessary

If CEPH_DIR is not PWD, echo export statements for CEPH_{CONF,KEYRING}.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>
Merge pull request #1969 from ceph/wip-vstart-conf

vstart.sh: echo CEPH_{CONF,KEYRING} exports if necessary

Reviewed-by: Sage Weil <sage@redhat.com>