Add timeout for I/O waitgroups

Closes #3286

This and a combination of a couple Docker changes are needed to fully
resolve the issue on the Docker side.  However, this ensures that after
processes exit, we still leave some time for the I/O to fully flush
before closing.  Without this timeout, the delete methods would block
forever.

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

runtime/v1/linux/proc/init.go

@@ -284,7 +284,7 @@ func (p *Init) Delete(ctx context.Context) error {
 }
 
 func (p *Init) delete(ctx context.Context) error {
-	p.wg.Wait()
+	waitTimeout(ctx, &p.wg, 2*time.Second)
 	err := p.runtime.Delete(ctx, p.id, nil)
 	// ignore errors if a runtime has already deleted the process
 	// but we still hold metadata and pipes