docker-py: override default API version to run all tests
docker-py: override default API version to run all tests

Otherwise some tests are skipped with the default API version
used:

    SKIPPED [1] tests/integration/api_service_test.py:882: API version is too low (< 1.38)
    SKIPPED [1] tests/integration/api_swarm_test.py:59: API version is too low (< 1.39)
    SKIPPED [1] tests/integration/api_swarm_test.py:38: API version is too low (< 1.39)
    SKIPPED [1] tests/integration/api_swarm_test.py:45: API version is too low (< 1.39)
    SKIPPED [1] tests/integration/api_swarm_test.py:52: API version is too low (< 1.39)

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

kojiromike/docker,cpuguy83/docker,thaJeztah/docker,paralin/docker,nawawi/docker,AkihiroSuda/docker,jimjag/docker,jameszhan/docker,vdemeester/docker,moul/docker,mahak/docker,bearstech/moby,konstruktoid/docker-upstream,gnailuy/docker,mahak/docker,yosifkit/docker,flavio/docker,AkihiroSuda/docker,Ramzec/docker,gnailuy/docker,dims/docker,mahak/docker,jameszhan/docker,ibuildthecloud/docker,jthelin/docker,paralin/docker,paralin/docker,justincormack/docker,nalind/docker,djs55/docker,flavio/docker,trebonian/docker,nawawi/docker,jameszhan/docker,jimjag/docker,Mokolea/docker,flavio/docker,nawawi/docker,konstruktoid/docker-1,thaJeztah/docker,docker/docker,vdemeester/docker,gnailuy/docker,jimjag/docker,moby/moby,konstruktoid/docker-upstream,AkihiroSuda/docker,Mokolea/docker,yosifkit/docker,mahak/docker,Mokolea/docker,nalind/docker,jimjag/docker,gnailuy/docker,dims/docker,bearstech/moby,dims/docker,konstruktoid/docker-upstream,konstruktoid/docker-upstream,Ramzec/docker,justincormack/docker,moby/moby,ibuildthecloud/docker,konstruktoid/docker-1,Mokolea/docker,estesp/docker,yosifkit/docker,nawawi/docker,kojiromike/docker,jthelin/docker,cpuguy83/docker,estesp/docker,estesp/docker,docker/docker,cpuguy83/docker,moul/docker,moul/docker,bearstech/moby,bearstech/moby,moul/docker,flavio/docker,konstruktoid/docker-1,djs55/docker,paralin/docker,trebonian/docker,justincormack/docker,nalind/docker,trebonian/docker,nalind/docker,vdemeester/docker,ibuildthecloud/docker,trebonian/docker,AkihiroSuda/docker,Ramzec/docker,thaJeztah/docker,yosifkit/docker,cpuguy83/docker,moby/moby,Ramzec/docker,kojiromike/docker,djs55/docker,thaJeztah/docker,docker/docker,ibuildthecloud/docker,moby/moby,ibuildthecloud/docker