gplazma2-jaas: add principal mutator plugin

JAAS plug in can be configured to use any jaas login module. As a
result we may get principas which can't be handles by gplazma. New
MutatorPlugin allows to convert some principals to supported equivalents.

in gplazma.conf:
auth jaas
...
map optional mutator gplazma.mutator.accept=org.apache.activemq.jaas.UserPrincipal gplazma.mutator.produce=username
map sufficient nsswitch
...

The supported output types:
   dn
   name
   username
   kerberos
   fqan

Ticket: #7763
Acked-by: Paul Millar
Target: trunk, 2.6, 2.2
Require-book: yes
Require-notes: yes