[JENKINS-25110] Update Jclouds to 1.8.0

This commit updates Jclouds plugin to use
Jclouds 1.8.0 and Guava 18.0.

Fixed CloseQuitely(), which is deprecated/removed
in Guava 18.0.
Merge pull request #74 from arun197/master

[JENKINS-25110] Update Jclouds to 1.8.0