network_manager: Upgrade delayed executor to be more generically useful

We can now use this in more parts of the codebase and with timeouts that
have more precision than 1 second.

Change-Id: I77c677230df6c288b29cd0895fe36f3f0158b393
Signed-off-by: William A. Kennington III <wak@google.com>
3 files changed