Adapt BWC version searching logic
Adapt BWC version searching logic

We were searching for what version to build the 6.7 branch with in BWC
builds by searching for a line starting with ES_BUILD_JAVA=java. Yet, on
the 6.7 branch we changed to using openjdk so this commit adapts that
logic accordingly.

vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,strapdata/elassandra,vroyer/elassandra,strapdata/elassandra