embargo: Add ability to lookup any NVR

MR artifacts have build NVR's like
"kernel-3.10.0-123.20.1.mr123_20150528_1233.el7". When a user inputs that
into embargo the result is a warning.

Enhance embargo to output a matching base build for any NVR.

Signed-off-by: Prarit Bhargava prarit@redhat.com