ipalib: Add DateTime parameter

Adds a parameter that represents a DateTime format using datetime.datetime
object from python's native datetime library.

In the CLI, accepts one of the following formats:
    Accepts LDAP Generalized time without in the following format:
       '%Y%m%d%H%M%SZ'

    Accepts subset of values defined by ISO 8601:
        '%Y-%m-%dT%H:%M:%SZ'
        '%Y-%m-%dT%H:%MZ'
        '%Y-%m-%dZ'

    Also accepts above formats using ' ' (space) as a separator instead of 'T'.

As a simplification, it does not deal with timezone info and ISO 8601
values with timezone info (+-hhmm) are rejected. Values are expected
to be in the UTC timezone.

Values are saved to LDAP as LDAP Generalized time values in the format
'%Y%m%d%H%SZ' (no time fractions and UTC timezone is assumed). To avoid
confusion, in addition to subset of ISO 8601 values, the LDAP generalized
time in the format '%Y%m%d%H%M%SZ' is also accepted as an input (as this is the
format user will see on the output).

Part of: https://fedorahosted.org/freeipa/ticket/3306

Reviewed-By: Jan Cholasta <jcholast@redhat.com>

ipalib/cli.py

@@ -46,11 +46,13 @@ import plugable
 from errors import (PublicError, CommandError, HelpError, InternalError,
                     NoSuchNamespaceError, ValidationError, NotFound,
                     NotConfiguredError, PromptFailed)
-from constants import CLI_TAB
+from constants import CLI_TAB, LDAP_GENERALIZED_TIME_FORMAT
 from parameters import File, Str, Enum, Any
 from text import _
 from ipapython.version import API_VERSION
 
+import datetime
+
 
 def to_cli(name):
     """
@@ -155,6 +157,8 @@ class textui(backend.Backend):
         """
         if type(value) is str:
             return base64.b64encode(value)
+        elif type(value) is datetime.datetime:
+            return value.strftime(LDAP_GENERALIZED_TIME_FORMAT)
         else:
             return value