[FAB-9244] 5.Client changes to get Idemix credential

This change set includes client side changes for getting
Idemix credential. Changes include:

1. Credential interface and implementation for X509
and Idemix credentials
2. Changes to the Client to handle send Idemix enrollment
request and handle the response from the server

Change-Id: I732883cd2949c72600c4348ca292cb60369315bd
Signed-off-by: Anil Ambati <[email protected]>

cmd/fabric-ca-client/command/main_test.go

@@ -1,17 +1,7 @@
 /*
-Copyright IBM Corp. 2017 All Rights Reserved.
+Copyright IBM Corp. All Rights Reserved.
 
-Licensed under the Apache License, Version 2.0 (the "License");
-you may not use this file except in compliance with the License.
-You may obtain a copy of the License at
-
-                 http://www.apache.org/licenses/LICENSE-2.0
-
-Unless required by applicable law or agreed to in writing, software
-distributed under the License is distributed on an "AS IS" BASIS,
-WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-See the License for the specific language governing permissions and
-limitations under the License.
+SPDX-License-Identifier: Apache-2.0
 */
 
 package command
@@ -2464,11 +2454,11 @@ func registerAndRevokeUsers(t *testing.T, admin *lib.Identity, num int) []*big.I
 			t.Fatalf("Failed to enroll the identity '%s': %s", userName, err)
 		}
 
-		cert, err := enrollResp.Identity.GetECert().GetX509Cert()
-		if err != nil {
-			t.Fatalf("Failed to get enrollment certificate for the user %s: %s", userName, err)
+		x509Cred := enrollResp.Identity.GetECert()
+		if x509Cred == nil || x509Cred.GetX509Cert() == nil {
+			t.Fatalf("Failed to get enrollment certificate for the user %s", userName)
 		}
-
+		cert := x509Cred.GetX509Cert()
 		revokeReq := &api.RevocationRequest{}
 		if i%2 == 0 {
 			revokeReq.Name = userName