MT#15709 api-cert-auth workaround for wheezy

this does not occur on docker (jessie)

Change-Id: Iaef6c93dc404c932b3ffa163010a3489a9bbeb34

t/api-rest/api-cert-auth.t

@@ -68,6 +68,7 @@ SKIP: {
 # successful auth
 $ua->ssl_opts(
     SSL_cert_file => $valid_ssl_client_cert,
+    SSL_key_file => $valid_ssl_client_key,
     SSL_verify_mode => 0,
     verify_hostname => 0,
 );