Feature: Support client outside domain

Until now, all clients had to be part of Kerberos domain as authentication
was done by mod_auth_kerb module of httpd by using Kerberos Ticket bundled
with the request.

To suport clients residing outside domain, we introduce a configurable option
called "auth_mode". When auth_mode is set to 'passive', a client residing
outside domain can authenticate itself by sending username(X-Auth-User) and
password(X-Auth-Key) as request headers. This information is gleaned from the
request and kinit is run against it. A successful kinit means the username
and password exists on the Kerberos server.

Change-Id: I1a165bd56bc3a425b00bcfdbf32150c14b5d9790
Signed-off-by: Prashanth Pai <ppai@redhat.com>
Reviewed-on: http://review.gluster.org/6296
Reviewed-by: Chetan Risbud <crisbud@redhat.com>
Tested-by: Chetan Risbud <crisbud@redhat.com>
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>
Additional Parameters to create keytab file

Minor changes to explicitly set keyversion number as 0 and
encryption method while creating keytab file on Windows AD server.
This has been noticed on different windows 2008 server that they set
different kvno by default. So just making sure it to be 0 as expected by
mod_auth_kerb.

Bug: N/A

Change-Id: Ic114e4964745abfe97fbfcd575b5205bd6aaf171
Signed-off-by: Chetan Risbud <crisbud@redhat.com>
Reviewed-on: http://review.gluster.org/6370
Reviewed-by: Prashanth Pai <ppai@redhat.com>
Tested-by: Prashanth Pai <ppai@redhat.com>
Reviewed-by: Luis Pabon <lpabon@redhat.com>