Restrict coverage output to all functest packages

Restrict coverage output to all functest packages

The next packages/modules are not yet covered:
  - functest/cli/setup.py
  - functest/core/pytest_suite_runner.py
  - functest/opnfv_tests/mano
  - functest/opnfv_tests/openstack/examples
  - functest/opnfv_tests/openstack/snaps
  - functest/opnfv_tests/openstack/vping
  - functest/opnfv_tests/sdn/onos
  - functest/opnfv_tests/vnf/aaa
  - functest/opnfv_tests/vnf/ims
  - functest/opnfv_tests/vnf/router
  - functest/utils/openstack

Change-Id: Id62749796864537615f0ca8b162ce77b6c1a3309
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>