travis: convert Ubuntu, CentOS & MinGW builds to use new make rules

travis: convert Ubuntu, CentOS & MinGW builds to use new make rules

Change the Travis CI configuration to invoke the new ci-build@$IMAGE
target instead of directly running Docker. This guarantees that when a
developer runs ci-build@$IMAGE locally, the container build setup is
identical to that used in Travis CI, with exception of the host kernel
and Docker version.

Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>