Based on the value of COMMON_ENABLE_OPENSTACK_INTEGRATION.

Installing requirements from the openstack role created role ordering
issues where openstack role had to run after the edxapp role so that the
required folders and the virtual environment are already created, BUT
edxapp migrations can also depend on the default file storage, which
will fail when using openstack storage if openstack requirements haven't
been installed yet.

Letting edxapp role install the requirements solves this problem.