ktest: Fix parsing of config section lines

The order for some of the keywords on a section line
(TEST_START or DEFAULTS) does not really matter. Simply need
to remove the keyword from the line as we process it and
evaluate the next keyword in the line. By removing the keywords
as we find them, we do not need to keep track of where on the
line they were found.

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