ipatests: Don't rely on certmonger's assigned request id
There are failure observed in test_rekey_keytype_DSA(test_cert.py)
It is due to the fact that there is no guarantee that the request id
will match the filename that certmonger assigns.
This fix assigns the request id with -I option to command (and make
use of existing fixture) and get the file name by grepping the
certmonger's directory with specified req id.
fixes: https://pagure.io/freeipa/issue/8725
Signed-off-by: Mohammad Rizwan <myusuf@redhat.com>
Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>