Prior to this commit, the docker login action assumed that if there was a password to authenticate with, Vagrant was using a host vm to run docker. This is likely due to some legacy decisions with how Vagrant used to manage running docker. This commit fixes that by only grabbing a host_vm lock if the host_vm is actually in use, otherwise login normally.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.