dim: Sanity checks for nightly.conf

Suggested by Chris Wilson and Jani Nikula.

To do this properly we need to again push the reading of nightly.conf
to be after the basic sanity checks, like it was before

commit 12976ee3
Author: Jani Nikula <jani.nikula@intel.com>
Date:   Fri Oct 28 12:40:46 2016 +0300

    dim: switch to using remote agnostic integration branch config

v2: Don't fail on setup.

v3: Rewrite and squash.

v4: Typing code with jetlag, hard it is.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>