Print exception if it's of type URLError (#946)

This prints the exception out if it's of type URLError when trying to
retrieve the default rosdep source list. This is intended to help others
debug #934 should they run into it.

Signed-off-by: Shane Loretz <[email protected]>

Author: sloretz

src/rosdep2/main.py

@@ -603,6 +603,7 @@ def command_init(options):
         data = download_default_sources_list()
     except URLError as e:
         print('ERROR: cannot download default sources list from:\n%s\nWebsite may be down.' % (DEFAULT_SOURCES_LIST_URL), file=sys.stderr)
+        print(e, file=sys.stderr)
         return 4
     except DownloadFailure as e:
         print('ERROR: cannot download default sources list from:\n%s\nWebsite may be down.' % (DEFAULT_SOURCES_LIST_URL), file=sys.stderr)