SLING-2847 : Installer integration tests fail due to unresolvable
artifacts

Since pax-exam does not support the maven.repo.local system property,
add support for it in OsgiInstallerTestBase.


git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1477870 13f79535-47bb-0310-9956-ffa450edef68