[SSSD] [PATCH] krb5_child: set debugging sooner

Both krb5_child and ldap_child would emit a "child started" message and only after that set up debugging to file. This might confuse users, because unless there is an error, the krb5_child.log might actually be empty. I'm thinking we might also add a couple of "tracing" DEBUG messages so that we can follow the flow in the subprocess more easily.