Hoist "Can we Fiber?" logic up to a helper function.
Hoist "Can we Fiber?" logic up to a helper function.

This also makes it possible to disable it in places where we were not
checking against the `METEOR_DISABLE_FS_FIBERS` env. variable, like in
`rm_recursive`.

Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor,Hansoft/meteor