Bazel: Make build tool chain forward compatible

Bazel 0.27 is going to flip incompatible Starlark flag:
--incompatible_string_join_requires_strings, see: [1] for
more details.

[1] https://github.com/bazelbuild/bazel/issues/7802

Bug: Issue 10998
Change-Id: Ibd6c77af8ed1ce5dc86ce88996003f7cf695aa08

tools/bzl/maven_jar.bzl

@@ -147,7 +147,7 @@ def _maven_jar_impl(ctx):
     out = ctx.execute(args)
 
     if out.return_code:
-        fail("failed %s: %s" % (" ".join(args), out.stderr))
+        fail("failed %s: %s" % (args, out.stderr))
 
     srcjar = None
     if ctx.attr.src_sha1 or ctx.attr.attach_source: