Merge pull request #2 from gcloud/providers

Adding Providers. Virtual Box is the first.
Fix some error conditions in vbox provider.
Updating readme.
Removing Provider reference from p.Server.
Refactoring the abstraction. Updating servers.
Adding images.
Use i in images_test and remove distribute.
Adding sizes and locations.
Adding travis badge.
Remove toml dependency.
Addig providers test.
Updating travis to test all packages.
Reformat imports in vbox/servers.
Add vbox/images.
Need to rig up a some skipping.
Refactoring provider.
Removing providers. They are in their own repo now.
Updating license and readme.
Using interfaces.
Updating travis to 1.2.