Increase injection timeout in itests (set to 20 seconds)

This fix sets timeout to 20 seconds (2 times de default value) in blueprint container injections. It is an intent to reduce the false-negatives test failures we had failing with:
gave up waiting for service org.osgi.service.blueprint.container.BlueprintContainer

Explanation about the timeout:
For other types [different than BundleContext], the Pax Exam injector tries to look up a service of the given type in the OSGi service registry. The lookup blocks while there is no matching service and fails the test if no service is found after a configurable timeout.
[since pax-exam 2.3.0] The @Filter annotation has an optional timeout argument, specifying the lookup timeout in milliseconds.
https://ops4j1.jira.com/wiki/display/paxexam/Dependency+Injection

itests now last arround 25 minutes to complete.
Add @SuppressWarnings(unused) to injected BlueprintContainers in itests.
Merge pull request #690 from isartcanyameres/fix/itests

Fix/itests