Fix hg tests

Our hg tests are failing because hg is installed in
/usr/local/bin but Bazel 0.21 only pass "/bin,/usr/bin" as PATH env
var.

With --test_env=PATH, the tests get the full environment.

Change-Id: Ie8efa9f8423642d45f1b8baae2eb5aa06cbe304f

.bazelrc

@@ -8,3 +8,4 @@ build --test_env='LC_ALL=en_US.UTF-8'
 build --jvmopt='-Dsun.jnu.encoding=UTF-8'
 build --jvmopt='-Dfile.encoding=UTF-8'
 build --test_env='LANG=en_US.UTF-8'
+test --test_env=PATH