Fix race condition in HystrixThreadPoolKey.asKey method

[daniilguit]

Fix rare case when this method would return different values for the same key

The problem would happen when:

1. Thread1: No such key when intern.get(name), so k was null
2. Thread1: We would enter if-statement
3. Thread2: Other thread would add key to intern map
4. Thread1: We will not put new key to intern map, but we will return newly created value instead of one stored in map

[chrisgray]

Should we make similar fixes to HystrixCommandGroupKey and HystrixCommandKey?

[daniilguit]

I think it worth to extract this functionality to new utility class. I can do this also and update pull request

[mattrjacobs]

This looks like a good change to me. Thanks @daniilguit ! Would you like me to merge this or wait until you're done with your refactoring?

[daniilguit]

Let's merge the final result, I will update pull request in a few days.

[daniilguit]

Committed code unification.

[mattrjacobs]

Thanks @daniilguit ! Looks great.