The legacy_config.py prints the UserWarning even the new config name is provided

[ironmanl]

The legacy_config.py prints the UserWarning even the new configuration name is provided. I can not remove the old names (Eg. REDIS_HOST) in the config as they have been used by another library.

The warning should be stopped if both "REDIS_HOST" and "RQ_DASHBOARD_REDIS_HOST" are provided, and it should not replace the "RQ_DASHBOARD_REDIS_HOST" with the value of the old config name.

| /opt/venv/lib/python3.6/site-packages/rq_dashboard/legacy_config.py:26: UserWarning: Configuration option REDIS_HOST is depricated and will be removed in future versions. Please use RQ_DASHBOARD_REDIS_HOST instead. | warnings.warn(warning_template.format(old_name=old_name, new_name=new_name), UserWarning) | /opt/venv/lib/python3.6/site-packages/rq_dashboard/legacy_config.py:26: UserWarning: Configuration option REDIS_PORT is depricated and will be removed in future versions. Please use RQ_DASHBOARD_REDIS_PORT instead. | warnings.warn(warning_template.format(old_name=old_name, new_name=new_name), UserWarning) | /opt/venv/lib/python3.6/site-packages/rq_dashboard/legacy_config.py:26: UserWarning: Configuration option REDIS_PASSWORD is depricated and will be removed in future versions. Please use RQ_DASHBOARD_REDIS_PASSWORD instead. | warnings.warn(warning_template.format(old_name=old_name, new_name=new_name), UserWarning) | /opt/venv/lib/python3.6/site-packages/rq_dashboard/legacy_config.py:26: UserWarning: Configuration option REDIS_DB is depricated and will be removed in future versions. Please use RQ_DASHBOARD_REDIS_DB instead.