Boto testcase to create, attach, detach and delete the volume

Description:
1. Create a volume and check its existence.
2. Create an instance.
3. Attach the volume to the instance.
4. Check the association of the instance to the volume ( Optional: we can run commands on instance to check attachment internally)
5. Detach the image from instance.
6. Check that the state of volume is "available" now.

We can extend the case by attaching multiple volumes to the same instance and check associations.