Invoke optional callback function on timer expiration

When the timer expires, it calls into it's own timeout
handler which matches with sd_event callback handler.

However, it is beneficial if the users of timer register
their own callback routine so that they can execute some
operations on timeout.

Change-Id: Ia88cb4e3c17f6dd8d4528fa193ec7927f083a92b
Signed-off-by: Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com>
4 files changed