Tighten UUID regexp used to check if a group is internal

The regular expression in AccountGroup.isInternalGroup() used
to determine whether a group identified by a particular UUID
is an internal Gerrit group was sloppy in that any UUID
containing a 40 (or more) character hex digit sequence anywhere
in the string was deemed an internal group. While very unlikely,
the expression could falsely match UUIDs from other systems.

Change-Id: Ie7cc56754bc11a6526fa1f35ea449e11b6c47a30
1 file changed