Downgrade conn for C* connections with versions beyond what we support (#379)

Fix for https://datastax-oss.atlassian.net/browse/NODEJS-634

Author: absurdfarce

lib/connection.js

@@ -254,8 +254,12 @@ class Connection extends events.EventEmitter {
 
           if (lowerVersion === self.protocolVersion) {
             lowerVersion = types.protocolVersion.getLowerSupported(self.protocolVersion);
-          } else if (types.protocolVersion.isBeta(self.protocol.version)) {
-            // Avoid downgrading the protocol version to a BETA protocol
+          } else if (!types.protocolVersion.isSupported(self.protocol.version)) {
+            // If we have an unsupported protocol version or a beta version we need to switch
+            // to something we can support.  Note that dseV1 and dseV2 are excluded from this
+            // logic as they are supported.  Also note that any v5 and greater beta protocols
+            // are included here since the beta flag was introduced in v5.
+            self.log('info',`Protocol version ${self.protocol.version} not supported by this driver, downgrading`);
             lowerVersion = types.protocolVersion.getLowerSupported(self.protocol.version);
           }
 

lib/types/protocol-version.js

@@ -49,6 +49,7 @@ const protocolVersion = {
   v3: 0x03,
   v4: 0x04,
   v5: 0x05,
+  v6: 0x06,
   dseV1: 0x41,
   dseV2: 0x42,
   maxSupported: 0x42,
@@ -64,14 +65,25 @@ const protocolVersion = {
     return ((version >= this.dseV1 && version <= this.dseV2));
   },
   /**
-   * Determines whether the protocol protocol version is supported by this driver.
+   * Returns true if the protocol version represents a version of Cassandra
+   * supported by this driver, false otherwise
+   * @param {Number} version
+   * @returns {Boolean}
+   * @ignore
+   */
+  isSupportedCassandra: function(version) {
+    return (version <= 0x04 && version >= 0x01);
+  },
+  /**
+   * Determines whether the protocol version is supported by this driver.
    * @param {Number} version
    * @returns {Boolean}
    * @ignore
    */
   isSupported: function (version) {
-    return (this.isDse(version) || (version <= 0x04 && version >= 0x01));
+    return (this.isDse(version) || this.isSupportedCassandra(version));
   },
+
   /**
    * Determines whether the protocol includes flags for PREPARE messages.
    * @param {Number} version