Add feature to mount host volumes

[maniSbindra]

What does this change

This change adds flag --mount-host-volume for commands like porter install and porter uninstall, which enables making a host file system folder available inside the running container, which executes the action.

For example the following commands makes the host's $HOME/.hostfolder folder available inside the bundle (as read/write mount) at /home/nonroot/.hostfolder .

porter install test-install --mount-host-volume "$HOME/.hostfolder:/home/nonroot/.hostfolder:rw"

Multiple folders may be mounted. Format for adding a mount is <host path>:<container path>[:<option>]. If option is ro or not provided or invalid, then file system is mounted as read only. If option is rw then file system is mounted as read/write inside the container

What issue does it fix

Closes #475

Notes for the reviewer

This works with the docker driver. By default folders are mounted as read only.

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR

[schristoff]

/azp run porter-integration

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[lbergnehr]

This is great! I would suggest, if it's not already there, to also enable mounting through the porter config. That way you vould set up mounts you always want, for example ~/.azure when doing Azure CLI authentication. Would be even more seamless.

[maniSbindra]

/azp run porter-integration