Use Timeout<> in the Listener class

Summary:
Communication classes use the Timeout<> class to specify the timeout. Listener
class was converted to chrono some time ago, but it used a different meaning for
a timeout of zero (Listener: infinite wait, Communication: no wait). Instead,
Listener provided separate functions which performed a non-blocking event read.

This converts the Listener class to the new Timeout class, to improve
consistency. It also allows us to get merge the different GetNextEvent*** and
WaitForEvent*** functions into one. No functional change intended.

Reviewers: jingham, clayborg, zturner

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D27136

llvm-svn: 288238