bitbake: toaster: enable required classes in the toaster startup script

bitbake: toaster: enable required classes in the toaster startup script

In order to use toaster, now you have to set INHERIT+="toaster buildhistory"
To keep it simple, I've done some changes in order to automate it. When toaster
is started, this line is added to a new file called toaster.conf.

This file is passed to the bitbake server with the --postread parameter.

Based on a patch by Cristiana Voicu <cristiana.voicu@intel.com>

(Bitbake rev: 029e868044989eda370340f8bf4200cfd2670fca)

Signed-off-by: Alexandru DAMIAN <alexandru.damian@intel.com>
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>