Check multiple ports from the docker exposed port range

In !4010 (merged), we started to check multiple ports from the exposed ports of a container.

However, whilst the health check command now supports this, there's a bug in the implementation where not all of the ports are provided to it.

When we parse the exposed ports, we only take the first port of any provided range. Therefore, whilst this would work:

EXPOSE 2375
EXPOSE 2376

This will not:

EXPOSE 2375 2376