This PR replaces use of time.After with a safe helper function
that creates a time.Timer to use instead. The new function returns
both a time.Timer and a Stop function that the caller must handle.
Unlike time.NewTimer, the helper function does not panic if the duration
set is <= 0.
Tests expect that as soon as eventer shuts down immediately on context
cancellations; but golang does not guarantee priority when multiple
pending channels are ready in a select statement.
This PR plumbs the plugins done ctx through the base and driver plugin
clients (device already had it). Further, it adds generic handling of
gRPC stream errors.
Seth Hoenig