JBIDE-16161 - Tycho tests require org.eclipse.osgi.compatibility.state fragment on Luna

This is a TEMPORARAY fix which is a workaround for https://bugs.eclipse.org/bugs/show_bug.cgi?id=417429
Use TP version 4.40.0.Alpha1
Parameterize jbosstools-site-stream (master | 4.2.luna)
Parent pom on stream 4.2.0.Alpha2
JBIDE-15760: Use newer version of facade plugin
Better factorization for signing

Rely on a skipSigning flag to avoid duplication of
signing/pack200 mojos.