Change file locking in devlist.hpp
Change file locking in devlist.hpp

Use timed_lock() instead of several try_lock()'s with random waiting
intervals.

Poulpy21/vexcl,Poulpy21/vexcl,Poulpy21/vexcl,ddemidov/vexcl,kapadia/vexcl,kapadia/vexcl,ddemidov/vexcl