Refactor destination checking block
Refactor destination checking block

This seperates out a helper method, and adds said method to run_reveiver
and run_sender methods in agents.py

Signed-off-by: jounaidr <f255539d5cd476e8f61551b6cd35c1f07b0f6698@stfc.ac.uk>

apel/ssm,apel/ssm