global: PACKAGES_EXCLUDE fix for testing+docker
global: PACKAGES_EXCLUDE fix for testing+docker

* Removes setting of PACKAGES_EXCLUDE in devsetup (used by Travis and
  Docker). Overriding this variable which is set by core Invenio or by
  an overlay is not a good idea.

Signed-off-by: Marco Neumann <3829486b93ec44395f0b980424bae9b6fb07b7bc@crepererum.net>

tiborsimko/invenio,inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio