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
Hardcoded values for range parameters such as base RID or range
size could be the reason the tests produced incorrect results,
as the ranges could get in conflict with already existing ranges
on the server.
Patch dynamically chooses ID and RID range space at the end of
all ranges already present on the server.
https://fedorahosted.org/freeipa/ticket/3662
