Fix mqtt logging and return values (#739)

api/error.go

@@ -4,3 +4,13 @@ import "errors"
 
 // ErrNotAvailable indicates that a feature is not available
 var ErrNotAvailable = errors.New("not available")
+
+// ErrTimeout is the error returned when a timeout happened.
+// Modeled after context.DeadlineError
+var ErrTimeout error = errTimeoutError{}
+
+type errTimeoutError struct{}
+
+func (errTimeoutError) Error() string   { return "timeout" }
+func (errTimeoutError) Timeout() bool   { return true }
+func (errTimeoutError) Temporary() bool { return true }