`make install.tools` already installs `gometalinter` (as can be seen in
the logs), so the subsequent `go get` steps are unnecessary.
This change also reorders the build directives according to execution
order: https://docs.travis-ci.com/user/customizing-the-build#The-Build-Lifecycle
and replaces the "before_install" step with an override of the default
"install" procedure (which we were suppressing anyway with install: true)
Signed-off-by: Jonathan Yu <jawnsy@redhat.com>
