Fix RakeOE::Config.release

Signed-off-by: Daniel Schnell <daniel.schnell.extern@ifm.com>
Fix default platform handling: there is no default platform anymore.
Platform has to be either defined via:

 * TOOLCHAIN_ENV environment variable
 * RakeOE::Config.platform


Signed-off-by: Daniel Schnell <daniel.schnell.extern@ifm.com>
Add RakeOE::Config#checks_pass? method

Signed-off-by: Daniel Schnell <daniel.schnell.extern@ifm.com>
Add more checks

Signed-off-by: Daniel Schnell <daniel.schnell.extern@ifm.com>
Description and prettier output

Signed-off-by: Daniel Schnell <daniel.schnell.extern@ifm.com>