Add script used to check failover process

[gregcorbett]

The added script checks the failover process is happening and not erroring.

It returns Icinga style return codes accordingly.

Rebasing once #8 has been merged should take care of the whitespace changes, in the mean time looking at the change without whitespace changes may be useful.

[gregcorbett]

@tofu-rocketry @jrha this isn't quite ready for a GitHub review (as it will be rebased at a later point), but please do take a look and leave comments 😄

[gregcorbett]

I've pushed a commit that ensures a text output, even if the script returns RETURN_CODE_OK, as Icinga needs this to generate notification emails.