Features rebuild fails when same features export also adds fields

When rebuilding features or when installing a Feature that contains both, an ECK entity type and new fields, the creation of these fields fails and one has to do another 'drush fra -y' after installation in order to get the expected results. This bug occurs due to the schema being cached and not being rebuilt until eck_init() is hit on the next page reload. The implementation in eck_init() is based on the expectation that, when adding a new ECK entity type, one always has another subsequent page reload before doing other thing. This is not true in case of Feature rebuilds.

The attached patch fixes this by doing a subsequent clean up and schema cache clear after installing exported ECK entity types.