Dockerfile changes to enable correct collectd functioning under alpine

[NeilCondon]

Proposed changes

Include packages and Dockerfile changes necessary to make collectd push metrics correctly (refer to #37). Update the docker-alpine project to build thin/edge 0.7.7 by default.

Types of changes

What types of changes does your code introduce to thin-edge.io? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New example (non-breaking change which adds functionality)
• [ ] Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• [ ] Documentation Update (if none of the other choices apply)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [x] I have read the CONTRIBUTING doc
• [ ] I have signed the CLA (in all commits with git commit -s)
• [ ] I have added necessary documentation (if appropriate)

Further comments

My mistake not to sign the commits individually - sorry.

[reubenmiller]

Closing as the docker-alpine example is being deprecated as the tedge-demo-container includes a more complete example showing how to use thin-edge.io in a container environment (both multi-service container and single process container setup)