Bazel: Support building with Java 9

Bazel: Support building with Java 9

Bazel@HEAD supports Java 9.

The current code has one single issue with Java 9 compliance: the usage
of javax.xml.bind.DatatypeConverter class for printHexBinary() method.
This class is not available on Java 9. One alternative is to use guava
library. Something similar was done here: [1]. But unlike the case with
checkstyle library, JGit currently doesn't use guava. Instead, we add
java.xml.bind module with --add-modules compiler option.

To build (or test) with Java 9, build custom bazel version and issue:

  $ bazel --host_javabase=/usr/lib64/jvm/java-9-openjdk build \
    --javacopt='--release 9' \
    --java_toolchain=@bazel_tools//tools/jdk:toolchain_jdk9 :all

The Java 9 support is backwards compatible.

* [1] https://github.com/checkstyle/checkstyle/issues/5027

Change-Id: I2c5203fc4e65885ce7b210f824fda85ba6d6c51d
Signed-off-by: David Ostrovsky <david@ostrovsky.org>