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/bazel_version.bzl b/tools/build/bazel/bazel_version.bzl
index 49434bf..9a0046e 100644
--- a/tools/build/bazel/bazel_version.bzl
+++ b/tools/build/bazel/bazel_version.bzl
@@ -16,12 +16,12 @@
 
 def check_bazel_version():
     if "bazel_version" not in dir(native):
-        fail("\nBazel version is too old; please use 0.23.* official release!\n\n")
+        fail("\nBazel version is too old; please use 0.27.* official release!\n\n")
     elif not native.bazel_version:
-        print("\nBazel is not a release version; please use 0.23.* official release!\n\n")
+        print("\nBazel is not a release version; please use 0.27.* official release!\n\n")
         return
 
     versions = native.bazel_version.split(".")
-    if not int(versions[1]) >= 23:
-        fail("\nBazel version %s is not supported; please use 0.23.* official release!\n\n" %
+    if not int(versions[1]) >= 27:
+        fail("\nBazel version %s is not supported; please use 0.27.* official release!\n\n" %
              native.bazel_version)