[8u40] post-commit review: RT-38485: [Quantum] Cleanup renderLock usage to call QuantumToolkit runWith/WithoutRenderLock

[Kevin Rushforth]

Post-commit review for:

JIRA:  https://javafx-jira.kenai.com/browse/RT-38485
Changeset:  http://hg.openjdk.java.net/openjfx/8u-dev/rt/rev/e0ac95b3aef1

Simple refactoring to move common code to a utility method in 
QuantumToolkit as a follow-up to 
https://javafx-jira.kenai.com/browse/RT-38289

-- Kevin