update test case for change in client-go (#419)

openwhisk-client-go is now validating X509 certificates when
they are loaded, so we have to provide files that actually are
a valid cert/key pair for this test cases to pass.

Author: dgrove-oss

tests/src/test/scala/org/apache/openwhisk/core/cli/test/WskConfigTests.scala

@@ -392,9 +392,9 @@ class WskConfigTests extends TestHelpers with WskTestHelpers {
           "--auth",
           "testKey",
           "--cert",
-          "cert.pem",
+          wskprops.cert,
           "--key",
-          "key.pem",
+          wskprops.key,
           "--apihost",
           "openwhisk.ng.bluemix.net",
           "--apiversion",