gplazma: update error message for forbidden properties

The configuration properties useGPlazmaAuthorizationModule and
useGPlazmaAuthorizationCell are forbidden as gPlazma always runs as a
cell.  The current error message is not obvious if this isn't
understood.  Unlike other error messages, it refers to running a
service, not using an alternative configuration option.

This patch updates the message to make this explicit.

Target: master
Patch: https://rb.dcache.org/r/7803/
Acked-by: Tigran Mkrtchyan
Requires-notes: yes
Requires-book: no
Request: 2.11
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7

skel/share/defaults/gplazma.properties

@@ -289,6 +289,25 @@ gplazma.htpasswd.file.cache-period.unit = SECONDS
 #
 #  The following properties are no longer supported.
 #
-(forbidden)useGPlazmaAuthorizationModule=Use gplazma.cell.export
-(forbidden)useGPlazmaAuthorizationCell=Use gplazma instead
 
+(forbidden)useGPlazmaAuthorizationModule = In this version of dCache gPlazma always \
+    runs as a cell and doors always contact a gplazma service.  To simulate \
+    useGPlazmaAuthorizationModule=true, run a non-exported gplazma service in the \
+    same domain as the door.  To simulate useGPlazmaAuthorizationModule=false and \
+    useGPlazmaAuthorizationCell=true, run an exported gplazma service somewhere in \
+    the dCache cluster.  To simulate useGPlazmaAuthorizationModule=false and \
+    useGPlazmaAuthorizationCell=false, run a non-exported gplazma service in the \
+    same domain as the door configured to use the local kpwd file.  For further \
+    details see the description of the gplazma.cell.name, <door>.service.gplazma \
+    (e.g., ftp.service.gplazma), and gplazma.cell.export properties.
+
+(forbidden)useGPlazmaAuthorizationCell = In this version of dCache gPlazma always \
+    runs as a cell and doors always contact a gplazma service.  If \
+    useGPlazmaAuthorizationModule=true then useGPlazmaAuthorizationCell property was \
+    ignored.  To simulate useGPlazmaAuthorizationModule=false and \
+    useGPlazmaAuthorizationCell=true, run an exported gplazma service somewhere in \
+    the dCache cluster.  To simulate useGPlazmaAuthorizationModule=false and \
+    useGPlazmaAuthorizationCell=false, run a non-exported gplazma service in the \
+    same domain as the door configured to use the local kpwd file.  For further \
+    details see the description of the gplazma.cell.name, <door>.service.gplazma \
+    (e.g., ftp.service.gplazma), and gplazma.cell.export properties.