Possible entrypoint addition?

[nwmcsween]

Problem:

Need a way to hook commands before commands are ran in containers that use alpine as a base to chown, create an account, etc. The Alpine image currently has no way of hooking this without 'forking' the image.

Solution:

create the dir/docker-entrypoint.d or less gross /etc/entrypoint.d and run scripts, etc before CMD, this may cause a slight regression in startup time due to sh execing sh again.

Thoughts?

[nwmcsween]

#173