Provide sane error message in case password is not found in configfile

Signed-off-by: Michal Čihař <michal@cihar.com>
Add keyring support

This makes osc2 compatible with current configs generated by osc.

Signed-off-by: Michal Čihař <michal@cihar.com>
- osc.cli.cli: minor changes and pep8-ified code