Modularize swift-auth CGI script, add unit tests

- Moved most of swift-auth CGI script to kerbauth_utils.py
- Added unit tests for kerbauth_utils.py
- Made MEMCACHE_SERVERS, DEBUG_HEADERS, TOKEN_LIFE as
  configurable parameters

Change-Id: I2e9e9823e8aa99dc2cf41327c55428350c8768dc
Signed-off-by: Prashanth Pai <ppai@redhat.com>
Reviewed-on: http://review.gluster.org/6248
Tested-by: Chetan Risbud <crisbud@redhat.com>
Reviewed-by: Chetan Risbud <crisbud@redhat.com>
Reviewed-by: Luis Pabon <lpabon@redhat.com>
Tested-by: Luis Pabon <lpabon@redhat.com>