[CORD-642] Support IPv6 in fabric emulation

Changes:
- Adds support IPv6 and autoconfiguration in the hosts
- Updates requirements.txt with the missing dep
- Extends mininet CLI with pingall6 cmd

Change-Id: Ieccdf6969d454c3720798b117d246bf0ae45292f
(cherry picked from commit b95002f4b8f81e350d16d577e7f447de97038021)
diff --git a/TestON/requirements.txt b/TestON/requirements.txt
index 86c8741..28f7503 100644
--- a/TestON/requirements.txt
+++ b/TestON/requirements.txt
@@ -11,3 +11,4 @@
 pylint==1.1.0
 requests==2.2.1
 scapy==2.3.1
+ipaddress==1.0.16