Add # patches_base magic comment to support rdopkg by default

[yazug]

It would be nice if when dlrn did builds it could add patches_base comment to the .spec after the Sources but before BuildArch

{noformat}
Source0: kuryr-lib-0.7.1.dev1-0.20171117165805.d8e39cd.tar.gz

patches_base=d8e39cd

BuildArch: noarch

{noformat}

[javierpena]

Is this something we still want? I understand we are already doing it downstream, but I can't figure out if we need it in DLRN.

[apevec]

we don't