setup should extract installer rather than build it.

[sallyom]

During CI runs, /bin/openshift-install from the libvirt image (binary build w/ libvirt tags) is scp'd over to gcp instance.
Instead, the openshift-baremetal-install binary should be extracted from the RELEASE_IMAGE_LATEST (from CI template) and then the OPENSHIFT_INSTALL_RELEASE_IMAGE_OVERRIDE is not required.

2 changes then:

1. the openshift-install build/update is no longer necessary in this setup (see provision.sh) but we need to add a default extracted binary from each release (at time of writing this would be 4.4 or 4.5 release)
2. CI template/libvirt CI image needs an update (outside of this issue)