Permit tls section for https config

When there is an untrusted CA signed cert in the chain (perhaps a
self-signed cert, for example) HTTPS requests will fail perhaps with
SELF_SIGNED_CERT_IN_CHAIN or UNABLE_TO_VERIFY_LEAF_SIGNATURE.

If you know you can trust the host `https` takes a `rejectUnauthorized`
config property that won't raise en error (like the `-k` flag for curl).

lib/schemas/minigun_test_script.json

@@ -22,7 +22,10 @@
         "mode": {
           "type": "string",
           "enum": [ "poisson", "uniform" ]
-        }
+        },
+        "tls": {
+          "type": "object"
+        },
       },
       "required": ["target", "phases"]
     },

lib/worker_http.js

@@ -56,13 +56,15 @@ function createRequest(requestSpec, config, ee) {
     var method = _.keys(requestSpec)[0].toUpperCase();
     var params = requestSpec[method.toLowerCase()];
     var uri = maybePrependBase(template(params.url, context), config);
-    var requestParams = {
+    var tls = config.tls || {};
+
+    var requestParams = _.extend(tls, {
       uri: uri,
       method: method,
       headers: {
       },
       timeout: 10 * 1000
-    };
+    });
 
     if (params.json) {
       requestParams.json = template(params.json, context);