ast-db-manage/cdr/env.py: Don't fail if a config file can't be loaded

ast-db-manage/cdr/env.py: Don't fail if a config file can't be loaded

When generating SQL files via the repotools alembic_creator.py script, a
configuration object is used programatically with SQLAlechemy, as opposed to
a configuration file. This patch ignores failures to interpret a config file,
as ... there isn't one in this case.

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@414763 65c4cc65-6c06-0410-ace0-fbb531ad65f3