RFR: 8243634: Add pandoc dependency when building linux-aarch64 at Oracle

[Mikael Vidstedt]

Add the explicit pandoc dependency since it may not be available on the build 
node.

JBS: https://bugs.openjdk.java.net/browse/JDK-8243634
webrev:  
http://cr.openjdk.java.net/~mikael/webrevs/8243634/webrev.00/open/webrev/

Cheers,
Mikael