MT#19043 decrypt: check for glusterfs 'mgmt-share' instead of 'shared_config'

We need to use some folder on glusterfs to ensure it is reachable.
/mnt/glusterfs/mgmt-share is good enough here as /mnt/glusterfs/shared_config
is no longer available.

Change-Id: I9f604db9604af41405cfd7b088abb332a463fe4d

scripts/decrypt

@@ -83,7 +83,7 @@ else
   fi
 fi
 
-if ! [ -d /mnt/glusterfs/shared_config ] ; then
+if ! [ -d /mnt/glusterfs/mgmt-share ] ; then
   log_warn "Looks like glusterfs is not running, can not install it automatically.
 
 Please execute the following command on one node