isisdae: stop spurious nagios warning

As a developer i would prefer the check for `ISISDAE Block Archive Status` test didn't give false results. This looks at the status of the `{PREFIX}DAE:_CHECK_ARCHIVER` PV which it expects to see as running. This PV is however updated when a run is ended, so until the first run is completed it will show an incorrect result.

## Acceptance criteria

PV does not trigger a spurious nagios warning when ibex is restarted
Test added to system tests

## To test

before change

start ibex server
verify that caget %MYPVPREFIX%DAE:_CHECK_ARCHIVER contains the word `Stopped`

after change

Repeat above and confirm it says Running