internal: Upgrade node in Vagrant test VM
internal: Initial import of persisted environment

This commit could almost be a standalone module as is.
internal: Add /env to test app
internal: Attach environment to commit

Environment is loaded from the Server instance and used for prepare and run.
Add env-set command to sl-pmctl

Restart goes through the existing replace mechanism which has been
updated to test for changes in environment. If the environment
variables of the replacement do not match the environment variables
of the current commit, then a hard restart is done instead of a soft
restart or replacement.
Add env-get command to sl-pmctl

Reads the environment variables stored in the strong-pm server. If
given, the pmctl client filters the list by name.
Add env-unset command to sl-pmctl

Internally add null as a special value for environment variables that
indicates deletion.

Expose this convention on the CLI as `sl-pmctl env-unset KEYS...`