Dirq sometimes failing to write temporary messages

[tofu-rocketry]

Following on from #62, while exception handling has been added in #63 for the missing IOError, these messages will still be lost, but they will be handled more nicely.

dirq seems to be sometimes failing when writing out accepted messages to the temporary directory it uses.

This could possibly be solved by retrying when adding the message to the accepted queue.

[tofu-rocketry]

https://github.com/apel/ssm/blob/3.2.1-1/ssm/ssm2.py#L323

[ElliottKasoar]

I wasn't able to reproduce the issue yesterday, but for next time, could we just do something like this?

try:
    name = self._inq.add({'body': extracted_msg,
                          'signer': signer,
                          'empaid': empaid})
except OSError:
    time.sleep(0.01)
    try:
        name = self._inq.add({'body': extracted_msg,
                              'signer': signer,
                              'empaid': empaid})
    except OSError as error:
        raise error

(Or more generally a for/while loop, although we would need an extra if statement to check for the last iteration.)