LDAP: Fix memory leaks in synchronous_tls_setup
We were never freeing "result" if it was allocated by
ldap_result(). We were also not freeing "errmsg" if it was
allocated but ldap_parse_result() returned an error.
Also disambiguate error messages from ldap_parse_result() and
error messages from sss_ldap_get_diagnostic_msg() since they use
differing memory-management functions.