bitbake: toaster: read database settings from the environment

bitbake: toaster: read database settings from the environment

We add the capability to read the database settings for
Toaster from the environment. The DATABASE_URL is intepreted
and used to override the default settings.

This capability is essential for easy deployment of Toaster
in a managed hosted environment, and for creating
build environments with custom database settings.

(Bitbake rev: d16d19dafb83448fc214fce4fbdc2bcbf4bf9ce3)

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