license.bbclass: optimize pkg runtime data

license.bbclass: optimize pkg runtime data

This fixes an ugly way I was trying to find pkg runtime
data for package and license manifest creation.

rootfs generation times for core-image-minimal:

Prior to patch
real	0m41.570s
user	1m40.466s
sys	0m6.768s

With patch
real	0m27.527s
user	0m9.833s
sys	0m3.496s

(From OE-Core rev: 664bbf3207c229eef5ef94a08713a652f33a8466)

Signed-off-by: Elizabeth Flanagan <elizabeth.flanagan@intel.com>
Conflicts:

	meta/classes/license.bbclass
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>