Call init and shutdown thread safely

[ivanpauno]

The rcl functions aren't thread safe.
The upper layer has to lock.

[jacobperron]

Out of curiosity, did this show up as errors somewhere?

Also, consider adding this to the Dashing and Eloquent patch release project boards for backport.

[ivanpauno]

Out of curiosity, did this show up as errors somewhere?

No, I realized about the problem in another discussion.
It's pretty hard to hit the problem, as shutdown should be called asynchronously while init is still running, which is an strange use-case.

[ivanpauno]

• Linux