This is a first pass to improve the way errors are handled and raised in
bundler's tests. The goal is to clean up tests and modernize them -
these were some obvious areas that could be cleaned up.

- Instead of raising "ZOMG" in the load error tests, it now tests for
the actual error and gem raising.
- Improve error messages where applicable.
- All errors raise a specific error class, rather than falling back to a
default and just setting a message.
- Removed arguments and `bundle_dir` option from `TheBundle` class as it wasn't
actually used so therefore we don't need to raise an error for extra
arguments.
- Removed error from `BundlerBuilder`, as it won't work if it's not
`bundler`, also it never uses `name`. The only reaon `name` is passed
in is because of metaprogramming on loading the right builder. I
think that should eventually be refactored.
- Replaced and removed `update_repo3` and `update_repo4` in favor of
just `build_repo3` and `build_repo4`. Rather than tell someone writing
tests to use a different method, automatically use the right method.

https://github.com/ruby/rubygems/commit/68c39c8451

Always build gems with RubyGems programmatically

https://github.com/ruby/rubygems/commit/5cc0c34e64

https://github.com/ruby/rubygems/commit/c3cc38c72c

Previous implementation included an empty element in the list of
deprecations.

https://github.com/rubygems/rubygems/commit/59eb233039

https://github.com/rubygems/rubygems/commit/3189d3e49b

When we need to reset system gems during specs, there's no need to
rebuild bundler, we can copy over the original gem home.

https://github.com/rubygems/rubygems/commit/7b4f80747b

Running everything in `bundled_app` by default causes the `bundled_app`
helper to be used everytime, and that will create a scoped bundled_app
folder if it does not exist. That causes `bin/rake spec:deps` to create
an empty `tmp/2.1/bundled_app` folder which is a bit weird.

This commit changes specs to not switch to a (possibly empty)
bundled_app directory when not necessary (for example, when running
`gem` commands in order to setup test dependencies).

https://github.com/rubygems/rubygems/commit/4bf89c0705

https://github.com/rubygems/rubygems/commit/8d4eb154b1

If you abort running test suite with a quick double Ctrl-C, tmp files
will be left around, and they will interfere with the next test run.

To avoid this, make sure to clear them once at the beginning of the test
suite.

### Before

```
$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
.............................................................................................^C^C

Finished in 19.45 seconds (files took 0.42722 seconds to load)
94 examples, 0 failures

(... turbo tests backtrace ...)

$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
.F....F....F...F......^C

Failures:

(... failures' details ...)
```

### After

```
$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
.................................................................................^C^C

Finished in 18.18 seconds (files took 0.4383 seconds to load)
82 examples, 0 failures

(... turbo tests backtrace ...)

$ bin/parallel_rspec
16 processes for 175 specs, ~ 11 specs per process
................................................................................^C^C

Finished in 8.79 seconds (files took 0.45187 seconds to load)
80 examples, 0 failures

(... turbo tests backtrace ...)
```

https://github.com/rubygems/rubygems/commit/6767a52711