ktest: New TEST_START instead of using [], and use real SHA1s

Change the config to use TEST_START where the options after a
TEST_START automatically get the [] as it is read and they do
not need to exist in the config file;

TEST_START
MIN_CONFIG = myconfig

is the same as

MIN_CONFIG[1] = myconfig

The benefit is that you no longer need to keep track of test numbers
with tests.

Also process the commit ids that are passed to the options
to get the actually SHA1 so it is no longer relative to the branch.
Ie, saying HEAD will get the current SHA1 and then that will
be used, and will work even if another branch is checked out.

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