Add a new gPlazma account phase plugin

gPlazma2 was still missing a simple way to ban users. This patch adds a
new plugin that allows blacklisting users based on <principal
type>:<value>
pairs given in a plain text file.

Example file:

---

alias name=org.dcache.auth.LoginNamePrincipal
alias dn=org.globus.gsi.jaas.GlobusPrincipal

ban dn:/C=XY/O=org/OU=Some Where/CN=Some One
ban javax.security.auth.kerberos.KerberosPrincipal:SOMEONE@SOMEWHERE.ORG
ban name:someone
ban dn:/C=XY/O=org/OU=Some Where/CN=Some One Else
ban javax.security.auth.kerberos.KerberosPrincipal:SOMEONEELSE@SOMEWHERE.ORG
---

Acked-by: Paul
Acked-by: Gerd
Target: master
Request: 2.6
Require-book: yes
Require-notes: yes
Patch: http://rb.dcache.org/r/5777/