Configure feature

[jercherng]

added functionality to configure target account interactively through the cli. There is also rudimentary regex to check for valid user input. I may have added the feature in bad form, when I added the calling method for 'configure' outside the scope of switch statement in bin/restacker. I did it so that we can call without having to initialize Restacker object bypassing need to login to configure yml file. To that end I also created the method as a singleton to the Restacker class so that we don't need to instantiate a Restacker object to use 'configure'. Did not configure for usage because the config_plane is set to ksp by default and I assumed that adding 'usage' when default config_plane is assumed would break intended functionality.

[godinezj]

+1

@jercherng, this is a great start to having a configurable restacker. Please change line 301 in restacker.rb to something like target = config.fetch(location, {}).fetch(:target) so that we keep compatibility with earlier ruby versions (Hash#dig() is a new addition).

In the future we will add the capability to add new configuration section and also configure each section's control plane configuration.

[jercherng]

all done, thank you for the advice.