Create a Certificate parameter

Up until now, Bytes parameter was used for certificate parameters
throughout the framework. However, the Bytes parameter does nothing
special for certificates, like validation, so this had to be done
for each of the parameters which were supposed to represent a
certificate.

This commit introduces a special Certificate parameter which takes
care of certificate validation so this does not have to be done
separately. It also makes sure that the certificates represented by
this parameter are always converted to DER format so that we can work
with them in a unified manner throughout the framework.

This commit also makes it possible to pass bytes directly during
instantiation of the Certificate parameter and they are still
represented correctly after their conversion in the _convert_scalar()
method.

https://pagure.io/freeipa/issue/4985

Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Martin Basti <mbasti@redhat.com>

ipaclient/remote_plugins/schema.py

@@ -12,6 +12,8 @@ import tempfile
 import types
 import zipfile
 
+from cryptography import x509 as crypto_x509
+
 import six
 
 from ipaclient.frontend import ClientCommand, ClientMethod
@@ -44,6 +46,7 @@ _TYPES = {
     'list': list,
     'tuple': tuple,
     'unicode': unicode,
+    'Certificate': crypto_x509.Certificate,
 }
 
 _PARAMS = {
@@ -57,6 +60,7 @@ _PARAMS = {
     'dict': parameters.Dict,
     'int': parameters.Int,
     'str': parameters.Str,
+    'Certificate': parameters.Certificate,
 }