ktest: Fix ELSE IF statements

The ELSE IF statements do not work as expected if another ELSE statement
follows. This is because the $if_set is not set. If the ELSE IF
condition is true, the following ELSE should be ignored. But because the
$if_set is not set, the following ELSE will also be executed.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>