Fix tagging within Dockerfile

[WillAyd]

When the user within a docker container does not match the user on the host machine (this is the case by default on Linux, not sure of all OSes) you cannot use git to inspect the worktree:

root@6de0debf3870:/home/pandas# git log
fatal: detected dubious ownership in repository at '/home/pandas'
To add an exception for this directory, call:

	git config --global --add safe.directory /home/pandas

This prevents builds within docker from being tagged with the appropriate git revision

[lithomas1]

Seems reasonable to me.

Thanks!

[mroeschke]

Thanks @WillAyd