Lowercase images names in Docker

I have noticed the docker hostname is case sensitive.

The container name (hostname) is docker-Linux.

ping docker-linux
Ping request could not find host docker-Linux. Please check the name and try again.

ping docker-Linux
64 bytes from docker-Linux (10.10.10.10): icmp_seq=1 ttl=64 time=0.053 ms

This was a design choice; technically, there should probably be no real issues with allowing mixed-case names, but we decided to stick with lowercase for now (which keeps the road open to allow uppercase characters in future, without breaking backward compatibility).