Mojo chokes on buggy/undefined nagios checks

[Barry Price]

Obviously they shouldn't exist in the first place, but Mojo doesn't cope well if a buggy charm has left half-defined check definitions on disk, e.g.:

command[check_haproxy_queue]=

This results in Mojo crashing with:

bash: line 7: syntax error near unexpected token `&&'
bash: line 7: `(set -x; && echo MOJO_NAGIOS_OK) || echo MOJO_NAGIOS_FAIL '

The linked MP should exclude any undefined/empty checks.

[Junien F (axino)]

I think it's good that Mojo chokes on these, it helps us identify charm bugs.

[Barry Price (barryprice)]

I think it's reasonable to inform the user about the issue, rather than crashing without an explanation.

As per MP, will rework to print a friendlier error in this situation.