CLOUDSTACK-4567: Correcting URLs that pointed to the incubator resources

The location on the downloads section points to the incubator pages and
the KEYS file used for GPG verify of the source points to the incubator
resource. Corrected both links

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
(cherry picked from commit 420b654eaf2fe23c28d0da8dbddd7c58d0ce868b)
CLOUDSTACK-840. DOC. New doc. Linked and full clones on VMware.