Testing building with Java 9 in our CI environment.

I've run `sbt publishLocal` on the CI server to make SBT 0.13.4-b646662
available. This includes changes to be compatible with Java 9.

I've also installed JDK9-ea on the CI server, and made it selectable
with `jvmSelect oracle 9`:

  scala/scala-jenkins-infra#221

Finally, I've used:

  https://github.com/retronym/java9-rt-export

to export a Java 8-style rt.jar to make scalac work without
needing native support for reading the jrt:// virtual filesystem
containing the standard library classes. Scala 2.12.1 and higher
support this, but SBT itself still uses Scala 2.10.6, so the shim
JAR is required.

This commit uses 0.13.4-b646662 for this build. The following
commit will sets an system property to instruct scalac to add the
rt.jar shim to the compilation classpath. I've split these steps
to help diagnose a failure.

r

Author: retronym

project/build.properties

@@ -1 +1 @@
-sbt.version=0.13.13
+sbt.version=0.13.4-b646662

scripts/common

@@ -19,7 +19,7 @@ mkdir -p $IVY_CACHE
 rm -rf $IVY_CACHE/cache/org.scala-lang
 
 SBT_CMD=${sbtCmd-sbt}
-SBT_CMD="$SBT_CMD -sbt-version 0.13.13"
+SBT_CMD="$SBT_CMD -sbt-version 0.13.14-b646662"
 
 # temp dir where all 'non-build' operation are performed
 TMP_ROOT_DIR=$(mktemp -d -t pr-scala.XXXX)