Replace Constants.PRODUCT_NAME with a startup option --product_name=bazel and 
(finally) delete Constants.java.

For bazel the file Constants.java is the only source of 
src/main/java/com/google/devtools/build/lib:common and since it was exporting
guava then many dependencies needed to be fixed.

--
MOS_MIGRATED_REVID=123648270

src/main/cpp/blaze.cc

diff --git a/src/main/cpp/blaze.cc b/src/main/cpp/blaze.cc
index bc6ba9c..a7dce22 100644
--- a/src/main/cpp/blaze.cc
+++ b/src/main/cpp/blaze.cc
@@ -549,6 +549,8 @@
                      globals->options.invocation_policy);
   }
 
+  result.push_back("--product_name=" + globals->options.GetProductName());
+
   globals->options.AddExtraOptions(&result);
 
   // The option sources are transmitted in the following format: