TESTS: replace hardcoded certificates
Since the hardcoded certificates have a limited lifetime they are
replaces by certificates from the test CA.
Related to https://pagure.io/SSSD/sssd/issue/3436
Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
(cherry picked from commit 0dc7f90667df6420bc9e93ae2c8bacd6ea148f0f
with fixes)