Disables visualization packages in the user environment by default.
Allows running leaner/faster import environments by default.
Packages can still be added with override or manually adding to environment.
The way in which Nixpks builds Ruby gems means that certain operations
by bundler *will not work*, namely `bundle install --redownload`.
According to the source the _cache/_ directory should have been kept,
however it seems through revisions to the file it has been purged.
Here was the comment from the original commit that introduced
buildRubyGem:
```
# Note:
# We really do need to keep the $out/${ruby.gemPath}/cache.
# This is very important in order for many parts of RubyGems/Bundler to not blow up.
# See https://github.com/bundler/bundler/issues/3327
```
Why is the _cache_ directory needed?
Bundler and RubyGems uses the cache as a source of truth.
When bundler executes `bundler install --redownload`, any gems it
discovers in the _GEM_PATH_ it assums must have their _.gem_ file
present in the cache (unaware it was installed from Nix).
Rather than downloading the gem from RubyGems the bundler code forcibly
re-installs the gem from the cache directory instead and **fails** if it
does not exist.
I've opened https://github.com/rubygems/rubygems/issues/4088 to see if
this failure should be soft and not so explicit; or fallback to fetching
the gem from scratch.
Without this change the following is the error:
```bash
> [nix-shell:~/code/nix/playground/jruby-bundler-rake]$ bundle install --force
[DEPRECATED] The `--force` option has been renamed to `--redownload`
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.jruby.ext.openssl.SecurityHelper (file:/nix/store/fis6nzrpw9pmcivr84qh5byfgm07qn10-jruby-9.2.13.0/lib/ruby/stdlib/jopenssl.jar) to field java.security.MessageDigest.provider
WARNING: Please consider reporting this to the maintainers of org.jruby.ext.openssl.SecurityHelper
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Fetching gem metadata from https://rubygems.org/.
Using bundler 2.1.4
Installing hello-world 1.2.0
Bundler::GemNotFound: Could not find hello-world-1.2.0.gem for installation
An error occurred while installing hello-world (1.2.0), and Bundler
cannot continue.
Make sure that `gem install hello-world -v '1.2.0' --source
'https://rubygems.org/'` succeeds before bundling.
```
Wth the fix the following no woccurs:
```bash
[nix-shell:~/code/nix/playground/jruby-bundler-rake]$ bundle install --redownload
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.jruby.ext.openssl.SecurityHelper (file:/nix/store/69wjlj4yirp48rv1q03zxgd4xvf0150d-jruby-9.2.13.0/lib/ruby/stdlib/jopenssl.jar) to field java.security.MessageDigest.provider
WARNING: Please consider reporting this to the maintainers of org.jruby.ext.openssl.SecurityHelper
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
Fetching gem metadata from https://rubygems.org/.
Using bundler 2.1.4
Installing hello-world 1.2.0
Bundle complete! 1 Gemfile dependency, 2 gems now installed.
Use `bundle info [gemname]` to see where a bundled gem is installed.
```
```
[nix-shell:~/code/nix/playground/jruby-bundler-rake]$ ls -l /nix/store/cwl9n5073hqgpfhnw4wic13nrrgg9dn8-gem-env/lib/jruby/gems/2.5.0/cache/
total 8
lrwxrwxrwx 1 fmzakari primarygroup 102 Dec 31 1969 bundler-2.1.4.gem -> /nix/store/ifc8a0gsfkrhkv953rd4rz8bcspahi8y-bundler-2.1.4/lib/jruby/gems/2.5.0/cache/bundler-2.1.4.gem
lrwxrwxrwx 1 fmzakari primarygroup 110 Dec 31 1969 hello-world-1.2.0.gem -> /nix/store/xi9ln6n1mz2is5ppykjxqhhkpjq9zm6i-hello-world-1.2.0/lib/jruby/gems/2.5.0/cache/hello-world-1.2.0.gem
```
I have a minimal project that demonstrates this issue at https://github.com/fzakaria/jruby-bundler-nix-failure
When overriding versions of build tools injected via hooks
`packageOverrides` was not taken into account and 2 incompatible
versions of the same package (`wheel` in this case) ended up in the
closure, causing the builds to fail.
