wic: add custom exception KickStartError

This exception will be raised by kickstart parser
on parsing errors and processed in the code which
calls parser to produce meaningful error output.

(From OE-Core rev: 13092793693c1c0ea172701578506f4a70a093d2)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/kickstart.py

@@ -31,6 +31,9 @@ from argparse import ArgumentParser, ArgumentTypeError
 
 from wic.partition import Partition
 
+class KickStartError(Exception):
+    pass
+
 def sizetype(arg):
     """
     Custom type for ArgumentParser