Removed the the vagrant-hostmanger plugin

This is not needed for virtualbox environment since we hardcode the IP address in the Vagrantfile for each VM.

The hostmanger plugin is required when using digital ocean droplets instead of virtualbox.

Digital ocean droplets are used in our snap-ci environment.

When using digital ocean droplets the IP address of the VPS can change when you destroy and rebuild the vps. The hostmanger plugin was used with the ansible skip-tag `static-hosts` to configure the `/etc/hosts` entries
Merge remote-tracking branch 'upstream/develop' into remove-hostmanger-plugin

Conflicts:
	docs/develop.md
removed refs to hostmanager and digital_ocean vagrant plugins
removed the vagrant box add step

running `vagrant up` will download the correct vagrant box if it is not already downloaded.

From note in pr #797
Merge pull request #800 from dolanjs/remove-hostmanger-plugin

Removed the vagrant-hostmanger plugin