Safer close and exchange check

Safer close and exchange check. Some heartbeat changes (which should not affect anything).

AMQP lib is the same 5.7.2 version.

To update:

1. Stop production.
2. Replace JAR file
3. Create temp Gateway (replace path and lib with FULL paths):

set java = "JAVA_HOME path"
set path = "RabbitMQjava.jar"
set lib  = "amqp-client-5.7.2.jar"
set sc=##class(isc.rabbitmq.Utils).CreateGateway(,java,path_";"_lib)
write $System.Status.GetErrorText(sc)

4. Update isc.rabbitmq.API:

set sc = ##class(isc.rabbitmq.Utils).UpdateJar(,path_";"_lib)
write $System.Status.GetErrorText(sc)

5. Start production.