[SPARK-13595][BUILD] Move docker, extras modules into external

## What changes were proposed in this pull request?

Move `docker` dirs out of top level into `external/`; move `extras/*` into `external/`

## How was this patch tested?

This is tested with Jenkins tests.

Author: Sean Owen <sowen@cloudera.com>

Closes #11523 from srowen/SPARK-13595.

1 files changed, 24 insertions, 0 deletions

diff --git a/external/java8-tests/README.md b/external/java8-tests/README.md
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index 0000000000..dc9e87f2ee
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+# Java 8 Test Suites
+
+These tests require having Java 8 installed and are isolated from the main Spark build.
+If Java 8 is not your system's default Java version, you will need to point Spark's build
+to your Java location. The set-up depends a bit on the build system:
+
+* Sbt users can either set JAVA_HOME to the location of a Java 8 JDK or explicitly pass
+  `-java-home` to the sbt launch script. If a Java 8 JDK is detected sbt will automatically
+  include the Java 8 test project.
+
+  `$ JAVA_HOME=/opt/jdk1.8.0/ build/sbt clean "test-only org.apache.spark.Java8APISuite"`
+
+* For Maven users,
+
+  Maven users can also refer to their Java 8 directory using JAVA_HOME. However, Maven will not
+  automatically detect the presence of a Java 8 JDK, so a special build profile `-Pjava8-tests`
+  must be used.
+
+  `$ JAVA_HOME=/opt/jdk1.8.0/ mvn clean install -DskipTests`
+  `$ JAVA_HOME=/opt/jdk1.8.0/ mvn test -Pjava8-tests -DwildcardSuites=org.apache.spark.Java8APISuite`
+
+  Note that the above command can only be run from project root directory since this module
+  depends on core and the test-jars of core and streaming. This means an install step is
+  required to make the test dependencies visible to the Java 8 sub-project.