New tool to store SQL connection configs locally (#218)

* added a new tool to store SQL connections locally. Modified the peek definition tests to create test database before running test


* fixed failing test QueryExecutionPlanInvalidParamsTest

* Fixes based on code review comments

* fixed failing test GetSignatureHelpReturnsNotNullIfParseInfoInitialized

test/Microsoft.SqlTools.ServiceLayer.Test.Common/TestCredentialService.cs

@@ -0,0 +1,98 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System.Collections.Generic;
+using System.Globalization;
+using Microsoft.SqlTools.ServiceLayer.Credentials;
+using Microsoft.SqlTools.ServiceLayer.Credentials.Contracts;
+
+namespace Microsoft.SqlTools.ServiceLayer.Test.Common
+{
+    public class TestCredentialService
+    {
+        private CredentialService credentialService = TestServiceProvider.Instance.CredentialService;
+
+        private static TestCredentialService instance = new TestCredentialService();
+
+        /// <summary>
+        /// The singleton instance of the service 
+        /// </summary>
+        public static TestCredentialService Instance
+        {
+            get
+            {
+                return instance;
+            }
+        }
+
+        private const string MSSQL_CRED_PREFIX = "Microsoft.SqlTools";
+        private const string TEST_CRED_PREFIX = "SqlToolsTestInstance";
+        private const string CRED_SEPARATOR = "|";
+        private const string CRED_SERVER_PREFIX = "server:";
+        private const string CRED_DB_PREFIX = "db:";
+        private const string CRED_USER_PREFIX = "user:";
+        private const string CRED_ITEMTYPE_PREFIX = "itemtype:";
+
+        /// <summary>
+        /// Read Credential for given instance Info. Tries the test credential id and if no password found
+        /// will try the MSSQL credential id
+        /// </summary>
+        public Credential ReadCredential(InstanceInfo connectionProfile)
+        {
+            var credentialParams = new Credential();
+            credentialParams.CredentialId = FormatCredentialIdForTest(connectionProfile);
+            Credential credential = credentialService.ReadCredential(credentialParams);
+            if (credential == null || string.IsNullOrEmpty(credential.Password))
+            {
+                credentialParams.CredentialId = FormatCredentialIdForMsSql(connectionProfile);
+                credential = credentialService.ReadCredential(credentialParams);
+            }
+
+            return credential;
+        }
+
+        /// <summary>
+        /// Stored the credential to credential store using the test prefix
+        /// </summary>
+        public bool SaveCredential(InstanceInfo connectionProfile)
+        {
+            Credential credential = new Credential(FormatCredentialIdForTest(connectionProfile), connectionProfile.Password);
+            return credentialService.SaveCredential(credential);
+        }
+
+        private string FormatCredentialIdForMsSql(InstanceInfo connectionProfile, string itemType = "Profile")
+        {
+            return FormatCredentialId(connectionProfile, itemType, MSSQL_CRED_PREFIX);
+        }
+
+        private string FormatCredentialIdForTest(InstanceInfo connectionProfile, string itemType = "Profile")
+        {
+            return FormatCredentialId(connectionProfile, itemType, TEST_CRED_PREFIX);
+        }
+
+        private string FormatCredentialId(InstanceInfo connectionProfile, string itemType = "Profile", string credPrefix = TEST_CRED_PREFIX)
+        {
+            if (!string.IsNullOrEmpty(connectionProfile.ServerName))
+            {
+                List<string> cred = new List<string>();
+                cred.Add(credPrefix);
+                AddToList(itemType, CRED_ITEMTYPE_PREFIX, cred);
+                AddToList(connectionProfile.ServerName, CRED_SERVER_PREFIX, cred);
+                AddToList(connectionProfile.Database, CRED_DB_PREFIX, cred);
+                AddToList(connectionProfile.User, CRED_USER_PREFIX, cred);
+                return string.Join(CRED_SEPARATOR, cred.ToArray());
+            }
+            return null;
+        }
+
+        private void AddToList(string item, string prefix, List<string> list)
+        {
+            if (!string.IsNullOrEmpty(item))
+            {
+                list.Add(string.Format(CultureInfo.InvariantCulture, "{0}{1}", prefix, item));
+            }
+        }
+    }
+}