Tarballs are generated on push and merge events.
push: Allows get a tarball from the PR and use locally.
merge: After a PR is merged we have a quick way to get latest
kata-tarball.
The tarball can be downloaded from github page only.
Fixes: #1710
Signed-off-by: Carlos Venegas <jos.c.venegas.munoz@intel.com>
