Add retry function for alarm REST notifier

The alarm REST notifier does not have retry function: notification simply
fails, for example, when the receiver is down. With this patch, retry
function for alarm REST notifier is added.

In some cases, alarm notifier can not get response even if the receiver is
working fine (e.g. temporarily lost connection, failing over).
Currently, alarm notifier give up to notify in that case.
So, this patch introduces ability to retry to alarm notifier.

By setting a unique request-id in HTTP request header (same id on retry),
the receiver can decide if the notification is new or redundant.

Change-Id: I29ee910e5beb5669377baaaa2810044a7c40d9ad
Closes-bug: #1329716