Bug 567993 - Contribute Flatpak process shim to Linuxtools

https://github.com/mbooth101/flatpak-dev-shim is crucial to enable
Eclipse running in Flatpak and being able to launch executables from the
host.
Let's have it as part of Linux Tools project to ease releasing.

Change-Id: Ia64e11ecfd3a6d61c1809103e7c8d9c8fde4ab7f
Signed-off-by: Alexander Kurtakov <akurtako@redhat.com>
Reviewed-on: https://git.eclipse.org/r/c/linuxtools/org.eclipse.linuxtools.eclipse-build/+/170933