ATLAS-3506 Add Expect 100 Continue header to Atlas Client.

Signed-off-by: Ashutosh Mestry <amestry@hortonworks.com>

client/common/src/main/java/org/apache/atlas/AtlasBaseClient.java

@@ -372,7 +372,8 @@ public abstract class AtlasBaseClient {
             // Set content headers
             requestBuilder
                     .accept(api.getProduces())
-                    .type(api.getConsumes());
+                    .type(api.getConsumes())
+                    .header("Expect", "100-continue");
 
             // Set cookie if present
             if (cookie != null) {