[ONOS-4797] Implement the Driver for handling Arista switch

Arista switch with its recent network OS, EOS, supports remote configuration & control. The protocol for this is Arista's proprietary but REST style.
Since ONOS has already REST southbound protocol, the control of Arista switch can be easily done by using this.

- Implemnted driver Loader for Arista switch
- Implemented DeviceDescriptionDiscovery for Arista switch
- [Deleted] Implemented the method sending post to Arista switch and return the result as a String

Change-Id: I9d4b8f0d707361949ff530ff414adb0437ae87d9
diff --git a/drivers/pom.xml b/drivers/pom.xml
index a70b1ff..3faccf9 100644
--- a/drivers/pom.xml
+++ b/drivers/pom.xml
@@ -43,6 +43,7 @@
         <module>bmv2</module>
         <module>corsa</module>
         <module>optical</module>
+        <module>arista</module>
     </modules>
 
     <!--<properties>