Fix the included Vagrantfile for running rspec tests

[timvisher]

In attempting to get a development environment set up to run the rspec
tests for a forthcoming PR I noticed that the Vagrantfile doesn't appear
to actually set up a functioning environment. I'm not sure when this
changed or how it's been missed but I figured I'd contribute a patch to
fix it up for my benefit and others.

In summary:

1. RVM no longer appears to be installed and configured the way the
   current provisioning script expects it be. Namely it requires users to
   be added to the rvm group rather than the sudo group and also
   requires a log out and then back in to finish setting up. In light of
   that I broke apart the provisioning into two separate shell scripts to
   get that 'log out and back in' behavior.
2. While I was there I tried to 'clean up' the script's logic, making it
   idempotent, using sudo -u vagrant -i rather than the su
   incantation, removing apparentyl unnecessary dependencies like
   build-essential and the GPG key, etc. I suspect there's some
   significant unnecessary complexity in the ruby version extraction but
   that could be tacked on later. This change is already big enough.

What do you think? I'm happy to cleanup the commits if there's interest in
the patch.

---

$ vagrant -v; VBoxManage -v
Vagrant 2.2.14
6.1.18r142142

Pre Change:

$ time {
    vagrant destroy -f &&
    vagrant up &&
    vagrant ssh-config |
      tee default.conf &&
    ssh -F default.conf default $'
      bash -lc \'
        hostname;
        date;
        cd /vagrant &&
          bundle exec rake; hostname
      \'
    '
  }
…
(Reading database ... 45709 files and directories currently installed.)
    default: Preparing to unpack .../git_1%3a2.17.1-1ubuntu0.8_amd64.deb ...
    default: Unpacking git (1:2.17.1-1ubuntu0.8) over (1:2.17.1-1ubuntu0.4) ...
    default: Setting up git (1:2.17.1-1ubuntu0.8) ...
    default: Ruby ruby-2.6.6 is not installed.
    default: -su: bundle: command not found
…

vagrant
Mon Apr 12 15:42:40 UTC 2021
bash: line 4: bundle: command not found
vagrant

real    3m7.343s
user    0m13.897s
sys     0m4.263s

Post Change:

$ time {
    vagrant destroy -f &&
    vagrant up &&
    vagrant ssh-config |
      tee default.conf &&
    ssh -F default.conf default $'
      bash -lc \'
        hostname;
        date;
        cd /vagrant &&
          bundle exec rake; hostname
      \'
    '
  }
…
Finished in 19 minutes 2 seconds (files took 3.09 seconds to load)
4674 examples, 0 failures, 3 pending

vagrant

real    26m21.810s
user    0m13.517s
sys     0m4.281s

[timvisher]

Ping on this. :)

[timvisher]

Ping on this. :)

[timvisher]

Last ping on this then I'll guess I'll close it assuming we're not interested.

[chrisroberts]

Sorry, for the delay on getting to this. Thank you!

[chrisroberts]

@timvisher if you would squash down the wip commits before we merge, that would be super 🙂

[timvisher]

Should be good to go. :)

[github-actions]

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