<oo-accept-node> Fix polyinstantiation sebool detection

Fedora 19 uses sebool identifier "polyinstantiation_enable" for the
option previously called "allow_polyinstantiation". This change allows
oo-accept-node to detect which version is being used to prevent a
false negative.
Merge pull request #3672 from dobbymoodge/fix-oo-accept-node

Merged by openshift-bot