Java versions for ci (elastic/x-pack-elasticsearch#4268)

* Add test matrix axis files for periodic java testing

* Add properties file defining java versions to use

Original commit: elastic/x-pack-elasticsearch@d679b9ab3e

.ci/java-versions.properties

@@ -0,0 +1,8 @@
+# This file is used with all of the non-matrix tests in Jenkins.
+
+# This .properties file defines the versions of Java with which to
+# build and test Elasticsearch for this branch. Valid Java versions
+# are 'java' or 'openjdk' followed by the major release number.
+
+ES_BUILD_JAVA=java10
+ES_RUNTIME_JAVA=java8

.ci/matrix-build-javas.yml

@@ -0,0 +1,2 @@
+ES_BUILD_JAVA:
+  - java10

.ci/matrix-java-exclusions.yml

@@ -0,0 +1 @@
+exclude:

.ci/matrix-runtime-javas.yml

@@ -0,0 +1,3 @@
+ES_RUNTIME_JAVA:
+  - java8
+  - java10