Fix status reason in events for deployment signals

When a signal is received and processed by a Resource, there could be an
event generated automatically. For such an event, Heat is supposed to
provide some useful message (including status_reason).  But currently,
the resource code can only process ceilometer alarms and watch rules,
for signals sent for a SoftwareDeployment resource, the signal is only
providing an string 'Unknown' as the status change reason.  This is
confusing when a user performs 'heat event-list stack'.

This patch adds an additional check (guess) whether the signal comes
from a SoftwareDeployment.  If that is the case, fill in the status
reason as 'deployment succeeded', or 'deployment failed (n)', where n is
the deploy_status_code that comes with the signal.

Closes-Bug: #1300679
Change-Id: Ic970a5dac923fffdcdd365983df58f4d338de849
Merge "Fix status reason in events for deployment signals" into stable/icehouse