Remove integration tests section from CONTRIBUTING.md
Remove integration tests section from CONTRIBUTING.md

This will be temporarily removed becuase the documentation is not
acurate.

The main reason is that some of the files generated when running the
tests need to be tracked but we don't have the right solution ATM.

cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release