tests: support running on platforms with old java

tests: support running on platforms with old java

In order to test on travis-ci's OSX setup, its easiest to support the old
version of Java that is installed there by default.  It is pretty old, so
it does not include the April 2017 update that disables MD5:

https://blogs.oracle.com/java-platform-group/oracle-jre-will-no-longer-trust-md5-signed-code-by-default
https://www.bleepingcomputer.com/news/security/oracle-to-block-jar-files-signed-with-md5-starting-with-april-2017
https://support.ca.com/us/knowledge-base-articles.TEC1691042.html

#292 #323