cert plugin: propagate the error for non-existent cert

ipa cert-show, ipa cert-revoke and ipa cert-remove-hold do not
print meaningful info when called on a non-existent cert id:
Certificate operation cannot be completed: Unable to communicate
with CMS

Propagate the reason from the HTTP message in order to print
'Certificate ID 0x.. not found'

Fixes: https://pagure.io/freeipa/issue/8704
Signed-off-by: Florence Blanc-Renaud <flo@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

ipaserver/plugins/dogtag.py

@@ -1471,6 +1471,7 @@ def get_certificate(self, serial_number):
         except errors.HTTPRequestError as e:
             self.raise_certificate_operation_error(
                 'get_certificate',
+                err_msg=e.msg,
                 detail=e.status  # pylint: disable=no-member
             )