SAMOA-76: changes JDK used for Travis builds

[mgrzenda]

SAMOA-76: changes JDK used for Travis builds

[mgrzenda]

Here is a brief summary of findings and solution:

1. oraclejdk7 is no longer available in Travis. Hence, the old Travis configuration failed.
2. openjdk7 was a suggested replacement
3. However, Travis builds based on openjdk7 are started, but never finish (are killed because of inactivity)
4. This kind of hanging build can be obtained also on standalone Linux/ mvn if _JAVA_OPTIONS are set as in Travis i.e. to "-Xmx2048m -Xms512m" and openjdk7 is used
5. Increasing memory limits in standalone mvn run resolves the problem 4), but not in Travis builds. Travis builds are still hanging in HDFS-related tests, as before even with less restrictive memory settings and forced garbage collection (see the list of commits to this JIRA issue for different options)
6. The ultimate working solution is to replace oraclejdk7 with oraclejdk8. This seems to be acceptable solution.

[mgrzenda]

Shall we apply this change of JDK7 to JDK8 to fix Travis builds?

[pwawrzyniak]

+1

[csterling]

It looks like this change is no longer sufficient. Newer builds are failing with an error indicating that Java feature-set 9 is the minimum requirement now. There may be other errors with the build after that is resolved. Requires further investigation.