ktest: Add IF and ELSE to config sections

Add IF keyword to sections within the config. Also added an ELSE
keyword that allows different config options to be set for a given
section.

For example:

TYPE := 1
STATUS := 0

DEFAULTS IF ${TYPE}
[...]
ELSE IF ${STATUS}
[...]
ELSE
[...]

The above will process the first section as $TYPE is true. If it
was false, it would process the last section as $STATUS is false.

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