Add flags -insecure, -user, -password, -suppress-missing-error
Add flags -insecure, -user, -password, -suppress-missing-error

Support to
- Self-signed cert
- Basic authentication
- Suppress errors for missing value

mackerelio/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins,mackerelio/mackerel-agent-plugins