Enforce build with Java 11 for all by default

- Build with JDK11 and language levels (source and target) are now
enforced in .bazelrc, which depends on our own Java toolchain (defined
in tools/build/bazel/BUILD)
- Easymock bumped to v4.0.2 with support for Java 11 (minor API changes)
- The minimum required Bazel version is now 0.27.*

Change-Id: I0bb6dfe7fc1ea134b5a53dd249c369d58259688c
diff --git a/tools/build/bazel/osgi_java_library.bzl b/tools/build/bazel/osgi_java_library.bzl
index 3720064..8296fcf 100644
--- a/tools/build/bazel/osgi_java_library.bzl
+++ b/tools/build/bazel/osgi_java_library.bzl
@@ -448,7 +448,7 @@
     if import_packages == None:
         import_packages = "*"
     tests_name = name + "-tests"
-    tests_jar_deps = list(depset(deps + test_deps)) + [name]
+    tests_jar_deps = depset(deps + test_deps).to_list() + [name]
     all_test_deps = tests_jar_deps + [tests_name]
     web_xml = _webapp()