RFR: JDK-8214910 If pandoc is present, markdown spec files should be processed

[Magnus Ihse Bursie]

If pandoc is available, specs should be built, even if full docs is not 
enabled.

Bug: https://bugs.openjdk.java.net/browse/JDK-8214910
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8214910-create-specs-if-pandoc-present/webrev.01

/Magnus