ipatests: fix TestIpaHealthCheckWithoutDNS failure
    
    TestIpaHealthCheckWithoutDNS is launched after
    TestIpaHealthCheck::test_ipa_healthcheck_expiring that is playing with
    the date. At the end of test_ipa_healthcheck_expiring, the date is
    reset using systemctl start chronyd but the date may need time to adjust
    and the subsequent tests may be launched with a system date set in the
    future.
    
    When this happens, dnf install fails because the certificate for
    the package repo is seen as expired, and TestIpaHealthCheckWithoutDNS
    fails.
    
    In order to avoid this issue, reset the date to the value saved at the
    beginning of the test.
    
    Fixes: https://pagure.io/freeipa/issue/8447
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>