Clean up crypto code, take advantage of new nss-python capabilities

This patch does the following:
- drops our in-tree x509v3 parser to use the python-nss one
- return more information on certificates
- make an API change, renaming cert-get to cert-show
- Drop a lot of duplicated code

ipapython/nsslib.py

@@ -188,7 +188,6 @@ class NSPRConnection(httplib.HTTPConnection):
         httplib.HTTPConnection.__init__(self, host, port, strict)
 
         logging.debug('%s init %s', self.__class__.__name__, host)
-        nss.nss_init_nodb()
 
         self.sock = io.Socket()
     def connect(self):