[tbot] Release 0.6.3

[Harald Seiler]

Hello all,

today tbot v0.6.3 is released! The major changes:

### Added
- `tbot.log.warning`: Print a warning message, similar to `message()`.
- If tbot fails to load a testcase source, it will now show the
  traceback that caused the failure, this should make development
  much easier because you don't have to guess what is wrong ...

### Changed
- Show any and all output that is received on the channel with `-vvv`.
  When debugging the boot process, it is valuable to know all data
  sent and received.
- `BoardLinuxMachine` now allows the login and password prompts to
  be clobbered.  This is the first step to solve the clobber issue.
- `BoardLinuxMachine` login now waits for the shell to respond.
  Previously, tbot just waited for a specified amount of time which
  lead to the login process sometimes failing.

### Removed
- `login_wait` config parameter from `BoardLinuxMachine`.  This "hack"
  is superseded by the more robust login implementation now.

### Fixed
- `importlib.util` needs to be manually imported on some python versions.
  Thanks Niel for stumbling upon this ;)

-- 
Harald

DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany
Phone: +49-8142-66989-62  Fax: +49-8142-66989-80   Email: hws at denx.de