"make test-docker" problematic with newer versions of Docker

[selfxp]

"make test-docker" command won't work using newer versions of Docker (tested with version 1.9)

ERROR: Service 'gateway' configuration key 'entrypoint' contains non unique items, please remove duplicates from ['prove', '-I', '/usr/local/test-nginx-0.24/lib', '-I', '/usr/local/test-nginx-0.24/inc', '-r', '/tmp/perl/']