Add MregCliLogger tests and fix logging configuration

[pederhan]

Adds some basic tests to ensure MregCliLogger behaves like we expect it to.

Forced logging reconfiguration

This PR also modifies MregCliLogger.start_logging() to use logging.basicConfig(..., force=true) to ensure the logger always re-runs basicConfig if called multiple times. This fixes a bug discovered by these tests, which caused the logger to not switch log files when a different log file path was passed in. This affected logging start when using the -filename option.

Docs for logging.basicConfig stating this behavior

Bug in action:

user@example.com> logging status
INFO > /tmp/mreg-cli.a3fp2t0p.360443/mreg-cli.log (7 lines, 857.0B)
user@example.com> logging start -filename /tmp/mreg-cli.a3fp2t0p.360443/mreg-cli.log.2
Logging started: INFO > /tmp/mreg-cli.a3fp2t0p.360443/mreg-cli.log.2
user@example.com> logging status
ERROR: Unable to read log file /tmp/mreg-cli.a3fp2t0p.360443/mreg-cli.log.2: [Errno 2] No such file or directory: '/tmp/mreg-cli.a3fp2t0p.360443/mreg-cli.log.2'

Since logging was already configured, logging.basicConfig silently skipped configuration, and thus did not create the new log file /tmp/mreg-cli.a3fp2t0p.360443/mreg-cli.log.2, causing an error when logging status attempts to read it.