Initial OpenEcomp A&AI Rest Client commit.

Change-Id: Ic6949778061bdf141431c4b14ea2417da6aa1e57
Signed-off-by: Shwetank Dave <shwetank.dave@amdocs.com>

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+# Common REST Client Library
+
+This library provides a single client implementation to be used by micro services for communicating via its REST API.
+
+---
+
+## Usage
+In order to make the _REST Client_ library available to your microservice, include the following dependency in your service's pom.xml:
+
+    <!-- Common REST Client Library -->
+    <dependency>
+        <groupId>org.openecomp.aai</groupId>
+        <artifactId>rest-client</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </dependency>
+    
+## Code Examples
+
+### Creating and Configuring a Client Instance
+In order to start talking to a service, you need to create a client instance and configure it.  The _RestClient_ uses a fluent interface which allows it to be both instantiated and configured as in the following example:
+
+    // Create an instance of the Rest Client and configure it.
+    RestClient myClient = new RestClient()
+        .validateServerHostname(false)
+        .validateServerCertChain(true)
+        .clientCertFile("certificate_filename")
+        .trustStroe("trust_store_filename")
+        .connectTimeoutMs(1000)
+        .readTimeoutMs(1000)
+        
+Note, that all of the above configuration parameters are optional and will be set to default values if they are not specified.
+
+### Querying The A&AI
+Once your service has a client instance, it can query the _Active & Available Inventory_ by specifying an HTTP endpoint, headers, and the expected response format:
+
+	MultivaluedMap<String, String> headers = new MultivaluedMapImpl();
+	headers.put("Accept", Arrays.asList(new String[]{"application/json"}));
+	headers.put("X-FromAppId", Arrays.asList(new String[]{"APP-ID"}));
+	headers.put("X-TransactionId", Arrays.asList(new String[]{UUID.randomUUID().toString()}));
+
+    OperationResult result = myClient.queryActiveInventory("http://some/endpoint", headers, RestClient.RESPONSE_MIME_TYPE.JSON);
+    
+    // You can also specify number of re-tries:
+    int retries = 3
+    OperationResult result = myClient.queryActiveInventory("http://some/endpoint", headers, RestClient.RESPONSE_MIME_TYPE.JSON, retries);
+
+         
+The result of the query is returned as an _OperationResult_ object, which can be unpacked in the following manner:
+
+The standard HTTP result code received back from the _A&AI_ is accessible as follows:
+
+    int resultCode = getResultCode()
+
+The actual result payload is accessible in the following manner:
+
+    String resultPayload = result.getResult()
+
+Finally, in the event of a failure, a failure cause message will be populated and can be accessed as follows:
+
+    String failureCause = result.getFailureCause()