ads-ioc docker image

Running an IOC:

# 
$ eval $(docker-machine env)
$ docker run -im pcdshub/ads-ioc:R0.6.1
epics>

Args to be passed to the adsIoc binary can be specified after the image name
above. For example:

$ docker run -im pcdshub/ads-ioc:R0.6.1 st.cmd

Updating ads-ioc-docker

Prior to updating ads-deploy, first update this docker image.

1. Tag and release ads-ioc
   a. Use the R0.0.0 style in accordance with module/IOC
      versioning standards
2. Update the Dockerfile
    a. Update any dependency versions that may have changed in the
       latest release
    b. If the ADS module itself has been updated, update
        `ADS_MODULE_VERSION`.
    c. Near the end of the Dockerfile, update `ADS_IOC_VERSION`.
       Note that this is separate from the other sections, as putting it
       near the top would cause an unnecessary rebuild of all dependencies
       upon update of the `ADS_IOC_VERSION`.
3. Rebuild
    ```
    $ export ADS_IOC_VERSION={version here}
    $ docker build -t pcdshub/ads-ioc:${ADS_IOC_VERSION} .
    $ docker build -t pcdshub/ads-ioc:latest .
    ```
4. Push
    ```
    $ docker push pcdshub/ads-ioc:${ADS_IOC_VERSION}
    $ docker push pcdshub/ads-ioc:latest
    ```
5. Commit, tag, and push to GitHub
    ```
    $ git tag ${ADS_IOC_VERSION}
    $ git push
    $ git push --tags
    ```