Use "gerrit" as the Gerrit user instead of "gerrit2"

We're still on Gerrit version 2.x but when we move to 3.0 it
will not make sense to have the user named "gerrit2".

Update all the documentation to refer to "gerrit" instead.

Also change the Jetty configuration to use "gerrit" instead.

Change-Id: I43a343669ac936b0585ee15e07d15643f9c3d6eb

Documentation/pgm-prolog-shell.txt

diff --git a/Documentation/pgm-prolog-shell.txt b/Documentation/pgm-prolog-shell.txt
index aee5799..a669aa7 100644
--- a/Documentation/pgm-prolog-shell.txt
+++ b/Documentation/pgm-prolog-shell.txt
@@ -36,8 +36,8 @@
 	         Copyright(C) 1997-2009 M.Banbara and N.Tamura
 	(type Ctrl-D or "halt." to exit, "['path/to/file.pl']." to load a file)
 
-	{consulting /usr/local/google/users/sop/gerrit2/gerrit/simple.pl ...}
-	{/usr/local/google/users/sop/gerrit2/gerrit/simple.pl consulted 99 msec}
+	{consulting /usr/local/google/users/sop/gerrit/gerrit/simple.pl ...}
+	{/usr/local/google/users/sop/gerrit/gerrit/simple.pl consulted 99 msec}
 
 	| ?- food(Type).