Contrail Software daemons' configuration files format

Contrail software daemons today accept configuration mostly via command line options. This can become quite cumbersome as the options list gets long. It is hard to read, edit, maintain, etc.

Instead, the options shall be read off both command line and a configuration file, and the overall options are thus consolidated. Command line options would take precedence over those that come from the config file.

The config file to process can be specified via a command line option --conf_file. By default, a daemon specific config file is is used from /etc/contrail/.

The config file is specified in the standard ini format. This is consistent with how openstack's configuration files are, as well.

e.g. control-node.conf

[DEFAULT]
# bgp_config_file=bgp_config.xml
# bgp_port=179
# hostip= # Resolved IP of `hostname`
# hostname= # Retrieved as `hostname`
# http_server_port=8083
# log_category=
# log_disable=0
# log_file=<stdout>
# log_file_size=10485760 # 10MB
# log_level=SYS_NOTICE
# log_local=0
# xmpp_server_port=5269

[COLLECTOR]
# port=8086
# server= # Provided by discovery server

[DISCOVERY]
# port=5998
# server=127.0.0.1 # discovery_server IP address

[IFMAP]
# certs_store=
# password=control-user-passwd
# server_url= # Provided by discovery server, e.g. https://127.0.0.1:8443
# user=control-user