Fix for broken renaming of scoped packages

[Ambroos]

Summary

I noticed that trying to rename a scoped package fails. After some investigation it turns out the regex in exotics/registry-resolver did not know what to do with scoped packages like "npm:@babel/register", or "npm:@babel/register@7.0.0-beta.32".

I simply had to add an @? for the @ right before the name capture group so the @ wouldn't result in everything after it being thrown into the version capture group (leaving name empty). That was the only thing required to get things to work.

I've added a test for it to the existing install renamed packages test, it seemed to make sense. As test package I used @turf/helpers since it'd been used as test package in other tests as well.

Context: From Babel 7 onwards packages are moved to the @babel scope. I was experimenting with upgrading one of our internal projects to Babel 7. The package babel-register is used as an optional peer dependency in other projects (like webpack, for automatically handling config.babel.js) via interpret. By adding @babel/register renamed to babel-register I could use the new version without having to wait for other package authors to update their packages.

Test plan

Before this PR:

Ambroos@Mac:~/Dev/temp $ yarn add --dev babel-register@npm:@babel/register@7.0.0-beta.32
yarn add v1.3.2
info No lockfile found.
[1/4] 🔍  Resolving packages...
error Received malformed response from registry for undefined. The registry may be down.
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.

After:

Ambroos@Mac:~/Dev/temp $ alias yarn="node ~/Dev/yarn/lib/cli/index.js"
Ambroos@Mac:~/Dev/temp $ yarn add --dev babel-register@npm:@babel/register@7.0.0-beta.32
yarn add v1.3.2
info No lockfile found.
[1/4] 🔍  Resolving packages...
[2/4] 🚚  Fetching packages...
[3/4] 🔗  Linking dependencies...
warning " > babel-register@7.0.0-beta.32" has unmet peer dependency "@babel/core@7.0.0-beta.32".
[4/4] 📃  Building fresh packages...
success Saved lockfile.
success Saved 20 new dependencies.
├─ babel-register@7.0.0-beta.32
...
└─ source-map@0.5.7
✨  Done in 1.56s.
Ambroos@Mac:~/Dev/player/temp $```

[Ambroos]

There seems to have been a problem with the test runners, as the tests should all pass. I can't rerun tests and don't want to make unnecessary changes. Could someone re-run them?

[waleedahmed3045]

Can the builds be triggered again for this PR? As it was a circleci issue.

https://discuss.circleci.com/t/unable-to-spin-up-environment/18109

[Ambroos]

I have rebased my work on master, tests seem to be (mostly) OK now.

[Gudahtt]

It looks like this has been fixed already, in this PR: #5229

[Gudahtt]

While this was fixed elsewhere, the additional integration test certainly couldn't hurt. The other PR had unit tests, but no integration test.