Allow Bazel to write to an external DIST_DIR (outside of OUT_DIR).

Also get Bazel to write real files there (not symlinks) so that the DIST_DIR can be independent.

Test: Manually using e.g. DIST_DIR=/tmp/foo USE_BAZEL=1 m dist
Change-Id: I39d5219500864c9ecc85f356a028e9b5bf2607f4
diff --git a/ui/build/rbe.go b/ui/build/rbe.go
index 64f3d4c..d9c33f6 100644
--- a/ui/build/rbe.go
+++ b/ui/build/rbe.go
@@ -74,7 +74,7 @@
 func getRBEVars(ctx Context, config Config) map[string]string {
 	vars := map[string]string{
 		"RBE_log_path":   config.rbeLogPath(),
-		"RBE_log_dir":    config.logDir(),
+		"RBE_log_dir":    config.rbeLogDir(),
 		"RBE_re_proxy":   config.rbeReproxy(),
 		"RBE_exec_root":  config.rbeExecRoot(),
 		"RBE_output_dir": config.rbeStatsOutputDir(),