Docker file doesn't included GRAALVM_HOME env variable and path to GRAAL JDK

[zaknuces]

I am mainly using GRAALVM via docker container. To ensure that graal enabled jdk is used, GRAALVM_HOME and GRAALVM_HOME/bin directories should be added to the PATH env variable.

Suggested changes:

1- Add GRAALVM_HOME env variable

ENV GRAALVM_HOME=/opt/graalvm-ce-$GRAAL_VERSION

2- Add GRAALVM and bin directory to PATH.

ENV PATH=GRAALVM_HOME:GRAALVM_HOME/bin:$PATH

Reason:
Run java -version before adding these paths, I am getting the following:
openjdk version "1.8.0_191" OpenJDK Runtime Environment (build 1.8.0_191-b12) OpenJDK 64-Bit Server VM (build 25.191-b12, mixed mode)

Run java -version after adding these paths.
openjdk version "1.8.0_192" OpenJDK Runtime Environment (build 1.8.0_192-20181024121959.buildslave.jdk8u-src-tar--b12) GraalVM 1.0.0-rc11 (build 25.192-b12-jvmci-0.53, mixed mode)