wic: use new syntax of 'except' statement

New syntax 'except Exception as err' is supported by Python >= 2.7.
Old syntax 'except Exception, err' is not supported by Python 3.

Used new syntax to be able to run wic on Python 3.

[YOCTO #9412]

(From OE-Core rev: 15e88714d6b0a93f72e8a19b083fcc1f2006e128)

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

scripts/lib/wic/plugin.py

@@ -97,7 +97,7 @@ class PluginMgr():
                             self.plugin_dirs[pdir] = True
                             msger.debug("Plugin module %s:%s imported"\
                                         % (mod, pymod.__file__))
-                        except ImportError, err:
+                        except ImportError as err:
                             msg = 'Failed to load plugin %s/%s: %s' \
                                 % (os.path.basename(pdir), mod, err)
                             msger.warning(msg)