Removed M2E induced classpath entry where a PDE entry already exists

M2E always inserts a classpath entry to appoint dependencies declared
in a POM. This is not desirable when working with PDE and a target
platform since it introduces ambiguities when M2E is enabled. This
commit removes all such entries.
Using bundle exec to execute rake tasks in integration tests
Use Import-Package instead of Require-Bundle for com.google.inject

Using Import-Package makes Geppetto agnostic to what bundle it is
that provides the injection packages. They are for instance also
provided by the sisu bundle from Sonatype (provided by the m2e
feature).

Closes #530