Initial work for dhcpd Dockerfile.

Hi,

here's a Dockerfile for dhcpd (DHCP server).
I think that this directory doesn't comply with the FHS. For reference: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Storage_Administration_Guide/s1-filesystem-fhs.html

I know this is only container, but think we should stick to the FHS when it's not causing any issues.

Think we could export /etc/dhcp and /var/lib/dhcpd/ - that would also educate the enduser about FHS proper places where dhcpd keeps it's stuff