test per-message-ttl dropped on dead lettering
look for the header under 'original-expiration'
Refactor per-message-ttl tests for dead lettered messages

Ensure the expiration property has been correctly removed.
Avoid modifying the global (static) MessageProperties.BASIC object
during test run.
Replace use of funny static initialiser and deprecated methods with the builder.
Merge bug25588
stable to default