Truncate status_reason to column length

This avoids a DataError "Data too long for column 'status_reason'"
when status_reason is longer than 255 chars.

This is implemented in the class StateAware which is extended
by Stack, Resource, and SoftwareDeployment.

Change-Id: I520803e54f9045fce2dc3b6a1b5c3be5052080aa
Closes-Bug: #1312815
Merge "Truncate status_reason to column length"