some bug fixes

[tcpan]

Hi,
I ran into a few bugs when trying to use the dropbox docker container, and I went ahead an fixed them (as far as I can tell):

1. switched to ubuntu base image, as it is officially supported by dropbox and also does not cause some warnings observed via "docker logs"
2. syntax of LABEL lines in Dockerfile was incorrect.
3. DEBIAN_DRONTEND line has been changed to ARG - this makes the variable a build time variable only.
4. installed tzdata, so that container can be started with --volume=/etc/timezone:/etc/timezone and --volume=/etc/localtime:/etc/localtime. This fixes the problem of host on local time zone and container defaulting to UTC. Dropbox probably is not checking time zones when comparing file timestamps, leading to file overwrites and data loss.

I ended up not using docker containers for dropbox, but thought I pass along these fixes. Please feel free to remove my username/email from the Dockerfile. Enjoy!

Tony

[otherguy]

Hi @tcpan! Thank you for your feedback and the effort you put into improving this!

My LABEL syntax is actually valid (so is yours of course) but I prefer the one with spacing to make the Dockerfile more readable.

Especially thanks for the change to the DEBIAN_FRONTEND variable and the tzdata feature! I did not think of that but you are right that it's absolutely crucial!

Instead of editing your PR, I have integrated your changes into a new PR #7.

Thanks again for your contribution!