Adding configuration file

[tdviet]

The fedcloudclient becomes more complex, there are many default values in the codes and environment variables. A configuration file ~/.config/fedcloud/fedcloud.ini could add some flexibility and simplify initial setting.

The configuration file could be useful for:

• overwriting default values of some constants in the codes: e.g. timeout, site configurations, ...
• being alternative of environment variables, e.g. default site and VO
• storing time of last update of site configurations
• and preparation for future features, e.g. location of SSH private keys for openstack ssh command

Example of use cases:

• users of some VOs/RIs may prefer to have a customized list of only sites supporting the VOs/RIs in fedcloudclient site configurations, not all sites registered in GOCDB. That can speedup all-sites operations.
• NGIs can have their own lists of sites

In both cases, simply change URL of site configuration in the fedcloud.ini file to the location of the customized site list is sufficient.

[tdviet]

The new fedcloud.config should read the config file and also environment variables, then set global variables including default site and VO according. That can work around the bug of requirement checking in the click-option-group lib mentioned in #150

[tdviet]

Configuration file is critical also for other issues:

• Improving certificate management #143 : Defining location for storing IGTF certificates, avoiding overwriting system certificates.
• Add logging  #142: Defining location of logfiles, avoiding writing logs to local directory or home directory

[tdviet]

Adding configuration file and related issues will need revisions of all components and may break some compatibilities. Therefore, a major version 2.0 will be released with all the changes together.

[tdviet]

First draft of config.py in branch 2.0-alpha: https://github.com/tdviet/fedcloudclient/blob/2.0-alpha/fedcloudclient/config.py