add JDK 11 community build

[SethTisue]

now that the JDK 10 build is up and running (#735), let's do 11 next

[SethTisue]

we should stop piling on behemoth 2 any further (it has all three 2.12 builds currently) and spread the jobs around more

UPDATE: I did some spreading around already. I should still choose carefully when adding this one

[SethTisue]

I tried a run locally and got EXTRACTION FAILED (failed: coursier, kxbmap-configs, scala-swing, slick)

scala-swing fix here: scala/scala-swing#82

[SethTisue]

I'll do another local run before we ship 2.12.7, and I'll scrutinize the results (that is, each individual failure reason, not just the overall greenness level) more closely than I have so far.

[SethTisue]

gah, --add-modules=java.xml.bind no longer works, so several projects (akka-more, scalafix, slick) don't even extract

EDIT: looks like this should work

-      // the usual thing some projects need on JDK 9
-      "--add-modules=java.xml.bind", "-XX:+IgnoreUnrecognizedVMOptions"
+    extra.settings: ${vars.base.extra.settings} [
+      // for JDK9+. one-deeper nesting level makes it apply to build definition
+      ["libraryDependencies += \"javax.xml.bind\" % \"jaxb-api\" % \"2.3.0\""]
+    ]

[SethTisue]

job created & assigned to behemoth 2: https://scala-ci.typesafe.com/view/scala-2.12.x/job/scala-2.12.x-jdk11-integrate-community-build/

[SethTisue]

OpenJDK 11 installed on behemoth 2 (using this as a template):

curl -O 'https://download.java.net/java/early_access/jdk11/28/GPL/openjdk-11+28_linux-x64_bin.tar.gz'
sudo mv openjdk-11+28_linux-x64_bin.tar.gz /usr/lib/jvm
cd /usr/lib/jvm
sudo tar xzf openjdk-11+28_linux-x64_bin.tar.gz
sudo rm openjdk-11+28_linux-x64_bin.tar.gz
sudo mv jdk-11 java-11-openjdk-x64
sudo update-alternatives --install /usr/bin/java java /usr/lib/jvm/java-11-openjdk-x64/bin/java 1
sudo update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/java-11-openjdk-x64/bin/javac 1

and in this new run: https://scala-ci.typesafe.com/view/scala-2.12.x/job/scala-2.12.x-jdk11-integrate-community-build/2/consoleFull

I now see Java home: /usr/lib/jvm/java-11-openjdk-x64 and dbuild is off and running

[SethTisue]

also made a 2.13 job: https://scala-ci.typesafe.com/job/scala-2.13.x-jdk11-integrate-community-build, assigned to behemoth 1, after following the same JDK installation steps as above

[SethTisue]

everything extracts now, at least, as of https://scala-ci.typesafe.com/view/scala-2.12.x/job/scala-2.12.x-jdk11-integrate-community-build/4/ . I had to fork coursier and kxbmap-configs to work around the JDK 11 .lines thing (scala/bug#11125), and I had to fork pcplod to remove Sam's sbt-sensible plugin, which had something somewhere in it that chokes on JDK 11

[SethTisue]

having a problems where dbuild shares ~jenkins/.dbuild even across multiple JDK versions, leading to cache consistency errors

dealt with it by shutting down all community build jobs on all 3 behemoths, blowing away ~jenkins/.dbuild on all 3 behemoths, installing JDK 11 on behemoth 3, and relocating the 2.12.x-jdk11 job from behemoth 1 to behemoth 3

a cleaner fix would be to have the run script or the config file somehow read the JDK major version being used and include it in some dummy setting so that dbuild would know it matters for reproducible-run purposes. /cc @cunei

UPDATE: I guessed wrong, that wasn't the cause. Toni fixed it in dbuild