Print both the implicit and explicit environment variables when running Bazel.

Test: Manually via USE_BAZEL=1 use_rbe m.
Change-Id: I9f0ac8875b47848fdea4ae97d107e4167c4a7f6e
diff --git a/ui/build/bazel.go b/ui/build/bazel.go
index 23b14ee..cc29aaf 100644
--- a/ui/build/bazel.go
+++ b/ui/build/bazel.go
@@ -169,8 +169,11 @@
 		fmt.Fprintf(bazelEnvStringBuffer, "%s=%s ", k, v)
 	}
 
-	// Print the full command line (including environment variables) for debugging purposes.
-	ctx.Println("Bazel command line: " + bazelEnvStringBuffer.String() + cmd.Cmd.String() + "\n")
+	// Print the implicit command line
+	ctx.Println("Bazel implicit command line: " + strings.Join(cmd.Environment.Environ(), " ") + " " + cmd.Cmd.String() + "\n")
+
+	// Print the explicit command line too
+	ctx.Println("Bazel explicit command line: " + bazelEnvStringBuffer.String() + cmd.Cmd.String() + "\n")
 
 	// Execute the build command.
 	cmd.RunAndStreamOrFatal()