Enabled non-root users to read nfs_shares.conf.

If you use the cinder NFS driver, it will create a file called
nfs_shares.conf, containing a list of NFS shares cinder can
use.  The file is created with 660 permissions and owned by
root:root.  When c-vol starts, it has problems reading
nfs_shares.conf, resulting in a "[Errno 13] Permission denied:
'/etc/cinder/nfs_shares.conf'".  This patch creates
nfs_shares.conf without using sudo, so c-vol can at least
read it.

Change-Id: Ifce2bd4b9ff2191445a1964c1ce09c823d096d68
Closes-Bug: #1297916
Merge "Enabled non-root users to read nfs_shares.conf."