Develop "mender config" tool for interactive configuration

We want to have a simple CLI tool to assist the user in configuring the device for Mender client to run on. We have decided to not depend on ncurses, so the tool will only use simple prompt-based input.

Acceptance criteria:

• The setup tool is created in mender-dist-packages repository
• The tool interactively ask the user for required input
• The tool checks for current values before overriding
• For the tenant token part, the tool will automatically fetch it from Hosted Mender using the user credentials
• The tool has a "sanity check" option that will verify the device is ready (see separate criteria for this)
• The tool takes optional parameters to skip the corresponding prompt
  • This will be the use case for the deb postinst script

Criteria for "device ready":

• There is valid string device_type
• There is a mender.conf file
• The mender.conf file has either TenantToken or ServerURL with values different than default ones