ipatests: test_trust: Add test to cover lookup of trusdomains

Adds an integration tests that checks that all trustdomains are
able to be found by trustdomain-find command right after the
trust has been established.

Also moves some code to allow easier adding common test cases for
both POSIX and non-POSIX test classes.

https://fedorahosted.org/freeipa/ticket/4208
ipalib: idrange: Make non-implemented range types fail the validation

The ipa-ipa-trust and ipa-ad-winsync ID Range types were allowed to
pass the validation tests, however, they are not implemented nor
checked by the 389 server plugin.

https://fedorahosted.org/freeipa/ticket/4323
trusts: Validate missing trust secret properly

Detect the situation if the user passes empty trust secret and
error out properly.

https://fedorahosted.org/freeipa/ticket/4266