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/capabilities.py

@@ -48,6 +48,9 @@ capabilities = dict(
 
     # primary_key_types: Non-unicode primary keys in command output
     primary_key_types=u'2.83',
+
+    # support for datetime values on the client
+    datetime_values=u'2.84'
 )