Require rid-base and secondary-rid-base in idrange-add after ipa-adtrust-install

Add a new API command 'adtrust_is_enabled', which can be used to determine
whether ipa-adtrust-install has been run on the system. This new command is not
visible in IPA CLI.

Use this command in idrange_add to conditionally require rid-base and
secondary-rid-base options.

Add tests to cover the new functionality

https://fedorahosted.org/freeipa/ticket/3634

API.txt

@@ -101,6 +101,10 @@ option: Str('version?', exclude='webui')
 output: Entry('result', <type 'dict'>, Gettext('A dictionary representing an LDAP entry', domain='ipa', localedir=None))
 output: Output('summary', (<type 'unicode'>, <type 'NoneType'>), None)
 output: Output('value', <type 'unicode'>, None)
+command: adtrust_is_enabled
+args: 0,1,1
+option: Str('version?', exclude='webui')
+output: Output('result', None, None)
 command: automember_add
 args: 1,7,3
 arg: Str('cn', cli_name='automember_rule')