Changes

[releng] Add reasonable build timeout to avoid hanging builds

The global timeout is set to 6 hours. In commit
[5bec3484](https://github.com/eclipse-sirius/sirius-desktop/commit/5bec34841cb72ed68a0e8244a19c25e85f5ad643),
the global timeout was removed because specific timeouts exist for
substages. It was observed that in some circumstances, this is not
enough. So a "big" global timeout is added to handle this case.

Signed-off-by: Fred G <frederic.gurr@eclipse-foundation.org>