tests/trust: Improved test coverage and execution.

This patch applies several changes to the ipatrust test playbook:

* Add externally defined parameters so execution in local trust
  environments can be configured. The available parameters are:
    * winserver_admin_password: the Administrator password for the AD
      server (default: 'SomeW1Npassword')
    * winserver_domain: the AD server domain (default: 'windows.local')
    * winserver realm: the AD server realm (by default, the uppercase
      version of winserver_domain)
    * ipaserver_domain: the FreeIPA server domain (default: 'ipa.test')
    * ipaserver_realm: the FreeIPA server realm (by default, the
      uppercase version of ipaserver_domain

* Modify trust verification to check for the existence of the trust as
  it the output of `ipa trust-find`, instead of cheking for the number
  of items returned, as the number might vary.

* Add idempotency tests by re-executing tasks and verifying that no
  change was performed.

* Added tests to verify creation of trusts with different 'range_type'.

* Use a Kerberos cache for shell scripts, and destroy it on exit.

* Properly remove all `idrange` that might be created upon setting up a
  trust.