Remove plugins before copying them again.

This way plugins can rename/delete files w/o having old files lying around.
Only delete core plugins.
Use PLUGIN_PATH in dokku default case.
port 'wait_to_retire' from broadly/dokku
Actually suppress the output from the git commands
Update vagrant installation instructions

Avoids 
```
Permission denied (publickey).
fatal: The remote end hung up unexpectedly
```
that can occur on certain Vagrant images. Since we need readonly anyway, might as well use HTTPS instead of SSH.
Merge pull request #718 from Coaxial/patch-1

Update vagrant installation instructions
Release 0.3.0
Use command instead of which for apt-get existential check in bootstrap.sh
Merge pull request #573 from Prelang/command-instead-of-which
Remove all references to Ubuntu 12.04. Refs #238

We no longer test against 12.04 VMs
Merge pull request #754 from progrium/remove-12-04
Setup dokku-installer within Vagrant VM on first provision
Merge pull request #699 from tombell/suppress-git-archive-all-output

Actually suppress the output from `git_archive_all`
Merge pull request #755 from progrium/vagrant-dokku-installer

Setup dokku-installer within Vagrant VM on first provision
Handle config values with spaces
Added test for config with spaces
Fixed setting config values with spaces over SSH
Add a set of spaces to prefix config variables when setting them
Merge pull-request #702 from jazzzz/config-spaces