Allow custom JAVA_BIN path

Since PuppetDB 6.11 Java 8, 9 and 10 are deprecated and Java 11 is
recommended. By default, the package use java from $PATH. This can
also be an older version. This patch adds a parameter that can be set to
a different java path, for example
/usr/lib/jvm/jre-11-openjdk/bin/java.