Update to latest Azure Compute api version and fix OS Image api

In the latest version of Azure, the image location field can actually hold semi-colon delimited list of locations. Moreover, there are two types of images, OS and VM. This PR avoids a namespace collision by renaming Image to OSImage. It also adjusts for images with multiple locations.
[minor] Use [`splitToList`](http://docs.guava-libraries.googlecode.com/git-history/v17.0/javadoc/com/google/common/base/Splitter.html#splitToList\(java.lang.CharSequence\))?