Added flavor in node object

Signed-off-by: Shashank Sahni <shredder12@gmail.com>
Nodes removal support

* API for removal added in v1.py
* job.remove() added in job.py
* cluster.remove_node() currently terminates the instances. For
better support and safe deletion, decommissioning of hadoop nodes
needs to be followed.
* Test for node removal added in job_test.sh

Signed-off-by: Shashank Sahni <shredder12@gmail.com>