Unified connection support (#765)

* Added the query to get big data cluster endpoints
Added bigDataClusterEndpoints to ObjectExplorerSession
Added bigDataClusterEndpoints to ServerInfo
Fixes some tests.

* Removed bigDataClusterEndpoints from session

* Since server property to get IsBigDataCluster is not implemented yet, use query of sys.asseblies instead to unblock us. Need to use server property when it is available
Add options to ServerInfo, so no need to change the contract in the further when adding new properties. Will move the existing properties to option later

* Undo changes not needed

* Resolved PR comments.

* Fixed node is null exception when can't find NodePath.

* Added comments

* Removed not used using

* Catch sqlException for the reader of BDC endpoints and set empty list to the option.

* Added comments for returning empty nodes.

src/Microsoft.SqlTools.ServiceLayer/Connection/Contracts/ServerInfo.cs

@@ -3,6 +3,9 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 //
 
+using System;
+using System.Collections.Generic;
+
 namespace Microsoft.SqlTools.ServiceLayer.Connection.Contracts
 {
     /// <summary>
@@ -64,5 +67,17 @@ namespace Microsoft.SqlTools.ServiceLayer.Connection.Contracts
         /// The Operating System version string of the machine running the SQL Server instance.
         /// </summary>
         public string MachineName { get; set; }
+
+        /// <summary>
+        /// Server options
+        /// </summary>
+        public Dictionary<string, object> Options { get; set; }
     }
 }
+
+public class ClusterEndpoint
+{
+    public string ServiceName;
+    public string IpAddress;
+    public int Port;
+}