releng: Build for Neon (4.6) by default

releng: Build for Neon (4.6) by default

As we are approaching the Neon release, we should compile and test
against Neon as our primary focus.

Change-Id: Ifdf3a1a8cdb700e0a2b98f3d519480face9b61b8
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/68848
Reviewed-by: Hudson CI
Reviewed-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Tested-by: Alexandre Montplaisir <alexmonthy@efficios.com>