Allow more than one open pipe at once.

This CL fixes that by adding a thread pool of max 8 threads. Trying to
open more file descriptors will block in a queue.

Test: Unit tests.
Bug: 33132744
Change-Id: Ide148e71cbf4948a59efc006285d22b8b9b958da
(cherry picked from commit b33955b04268566c1d921b09ceb1f8fe413d7aa2)
1 file changed