Add support for docker run --tmpfs flag.

[khimaros]

This adds support for the docker run --tmpfs flag as described in #2778

[GordonTheTurtle]

Please sign your commits following these rules:
https://github.com/docker/docker/blob/master/CONTRIBUTING.md#sign-your-work
The easiest way to do this is to amend the last commit:

$ git clone -b "master" git@github.com:sllawap/compose.git somewhere
$ cd somewhere
$ git commit --amend -s --no-edit
$ git push -f

Ammending updates the existing PR. You DO NOT need to open a new one.

[khimaros]

@GordonTheTurtle -- should be all set now. Sorry for the oversight; first time contributor!

[dato]

I tried to test this PR, because I wanted to check whether syntax like /tmp:size=10M or /home/foo/tmp:uid=NNN would work.

However, I did not manage to run the PR (see error below). I think support for tmpfs is needed in docker-py, maybe?

Consider the following docker-compose.yml:

version: "2"

services:
  test:
    image: busybox
    tmpfs: /run
    network_mode: none

I run:

$ env PYTHONPATH=. bin/docker-compose up test

It fails with:

Traceback (most recent call last):
  File "bin/docker-compose", line 3, in <module>
    main()
  File ".../src/compose/compose/cli/main.py", line 56, in main
    command.sys_dispatch()
  […]
  File ".../src/compose/compose/service.py", line 648, in _get_container_host_config
    tmpfs=options.get('tmpfs'),
  File ".../Library/Python/Envs/compose/lib/python2.7/site-packages/docker/api/container.py", line 141, in create_host_config
    return utils.create_host_config(*args, **kwargs)
TypeError: create_host_config() got an unexpected keyword argument 'tmpfs'

I looked at the AppVeyor logs, but I didn’t see the test_tmp() test run, only the simpler test_tmpfs_option(). I don’t really know if it the test was supposed to catch it or not.

[dnephin]

Since this can be a list or a string it needs to be in the list with dns and dns_search just below this line.

[dnephin]

Thanks for the PR!

I've left one comment about a fix.
You'll also need to rebase on master, squash to one commit, and make sure that commit is signed.

If this requires a specific pre-release version of docker-py you can update the required version in requirements.txt. We're currently using a pinned version, so you might not need to make any changes there.

[dnephin]

Carried in #3137

[khimaros]

@dnephin sorry for neglecting this, I was on vacation. Thank you for pushing this through!