MFH: r522784

databases/db6, db5: fix JAVA-enabled build, suppress sed failed warnings

Add JAVA_VERSION="7 8" to db6
Add REWARNFILE=/dev/null to db6 and db5

Reported by: Tommy P <tommyhp2@gmail.com>
PR: 243278

Approved by: ports-secteam (blanket, unbreaks a broken build under non-default JAVA option)