classes/rootfs_rpm: implement BAD_RECOMMENDATIONS for RPM

classes/rootfs_rpm: implement BAD_RECOMMENDATIONS for RPM

Add support for the BAD_RECOMMENDATIONS variable that can be used to
prevent specific packages from being installed via an RRECOMMENDS
relationship when using the RPM backend. (Previously this
functionality was only available when using ipk packaging.)

In the process this moves the defaulting of BAD_RECOMMENDATIONS (as
empty) to bitbake.conf since it is no longer specific to the ipk
backend, as well as unifying some of the code that creates the
configuration for smart for use on the host and target.

Fixes [YOCTO #3916].

(From OE-Core rev: 4e85129a7d47baf3e32b815cbc277bff84e085a0)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>