Update tox to skip sdist step and speed up the build.
Update tox to skip sdist step and speed up the build.

ByteInternet/libcloud,andrewsomething/libcloud,ByteInternet/libcloud,andrewsomething/libcloud,Kami/libcloud,mistio/libcloud,apache/libcloud,andrewsomething/libcloud,apache/libcloud,mistio/libcloud,Kami/libcloud,apache/libcloud,mistio/libcloud,Kami/libcloud,ByteInternet/libcloud