Allow runtime contributions inside rest-api fragment

When defining a module contributing to the rest api (like https://github.com/nuxeo/nuxeo/tree/master/nuxeo-features/rest-api/nuxeo-web-resources-rest or https://github.com/nuxeo/nuxeo-platform-document-routing/tree/master/nuxeo-routing-rest-api), the following is added to the MANIFEST.MF file:

Fragment-Host: org.nuxeo.ecm.platform.restapi.server

It seems this registration conflicts with Nuxeo-Component registration of contributions to the Nuxeo runtime: contributions are ignored.