Unset restrictive umask before creating files (#908)

If a user has a restrictive umask (for example 0077) set, it will be
inherited to sudo and thus files created with sudo where not readable by
the normal user. In that case, when setting up a new chroot, the
etc/apk/repositories file would have umask 600 and a os.path.exists()
(in update_repository_list) would return false. Setting the umask to 022
(octal) first, results in world readable files and directories, so the
user running `./pmbootstrap.py install` can read them.

pmb/__init__.py

@@ -35,6 +35,7 @@ def main():
     # Parse arguments, set up logging
     args = parse.arguments()
     pmb_logging.init(args)
+    os.umask(0o22)
 
     # Wrap everything to display nice error messages
     try: