tests service: Fixes evaluation of 'Keytab = True'

In ansible-core 2.19 there's no automatic coercion from None or empty
strings to the boolean value "false", so we need to compare the result
of the filter 'regex_search' to 'None' and the empty string to evaluate
if any match occurred.

In fixing this issue, it was found that the tests were incorrectly
evaluating the results, and the comparisons were fixed.

Signed-off-by: Rafael Guterres Jeffman <rjeffman@redhat.com>