wic: refactored processing of wic exceptions

All wic exceptions are now inherited from new base exception
class WicError. It makes them easy to maintain and catch.

Processing of exceptions is done this way:
    Known wic exceptions cause wic to print error message to stdout.
    Unknown exceptions are not catched anymore and produce standard
    python traceback.

(From OE-Core rev: e5e2c18ce4344c14d9e52ece916333bd0a619281)

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

scripts/lib/wic/utils/errors.py

@@ -16,32 +16,14 @@
 # with this program; if not, write to the Free Software Foundation, Inc., 59
 # Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 
-class CreatorError(Exception):
-    """An exception base class for all imgcreate errors."""
-    keyword = '<creator>'
+class WicError(Exception):
+    pass
 
-    def __init__(self, msg):
-        self.msg = msg
+class CreatorError(WicError):
+    pass
 
-    def __str__(self):
-        if isinstance(self.msg, unicode):
-            self.msg = self.msg.encode('utf-8', 'ignore')
-        else:
-            self.msg = str(self.msg)
-        return self.keyword + self.msg
+class Usage(WicError):
+    pass
 
-class Usage(CreatorError):
-    keyword = '<usage>'
-
-    def __str__(self):
-        if isinstance(self.msg, unicode):
-            self.msg = self.msg.encode('utf-8', 'ignore')
-        else:
-            self.msg = str(self.msg)
-        return self.keyword + self.msg + ', please use "--help" for more info'
-
-class KsError(CreatorError):
-    keyword = '<kickstart>'
-
-class ImageError(CreatorError):
-    keyword = '<mount>'
+class ImageError(WicError):
+    pass

scripts/wic

@@ -53,6 +53,7 @@ else:
     bitbake_main = None
 
 from wic.utils.oe.misc import find_bitbake_env_lines, set_bitbake_env_lines
+from wic.utils.errors import WicError
 from image import engine
 from image import help as hlp
 
@@ -309,10 +310,8 @@ def main(argv):
 
 if __name__ == "__main__":
     try:
-        ret = main(sys.argv[1:])
-    except Exception:
-        ret = 1
-        import traceback
-        traceback.print_exc()
-    sys.exit(ret)
+        sys.exit(main(sys.argv[1:]))
+    except WicError as err:
+        print >> sys.stderr, "ERROR:", err
+        sys.exit(1)