Eventscripts: 10.interfaces clean-up - use more descriptive variable names.

Eventscripts: 10.interfaces clean-up - use more descriptive variable names.

The name of variable $ok gives no clue to its meaning/use so this
changes that variable to be named $up_interfaces_found.

The return logic relating to $ok and $fail is difficult to read, so
these variables are given true/fale values, allowing the return logic
to be simplified.

Signed-off-by: Martin Schwenke <martin@meltin.net>