tc: save model runtime logs

This change includes:
* Saving fvp model run logs into the files form different terminals
* Introduced a new argument used as suffix to give custom name to the
  log directory. This is to differentiate special case logs from the
  regular logs.
  Ex: Logs to be shared with other teams.

Signed-off-by: Rupinderjit Singh <rupinderjit.singh@arm.com>