Add --skip-config flag to soong_ui.bash

--skip-config can be combined with --soong-only to skip creating
soong.variables from Make, allowing a custom soong.varibles.

Test: manual
Change-Id: Iee9bfa4efeed801339e7c3c1e4807709485e701a
diff --git a/ui/build/config.go b/ui/build/config.go
index 220e734..b9aaaf8 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -573,6 +573,9 @@
 		} else if arg == "--skip-ninja" {
 			c.skipNinja = true
 		} else if arg == "--skip-make" {
+			// TODO(ccross): deprecate this, it has confusing behaviors.  It doesn't run kati,
+			//   but it does run a Kati ninja file if the .kati_enabled marker file was created
+			//   by a previous build.
 			c.skipConfig = true
 			c.skipKati = true
 		} else if arg == "--skip-kati" {
@@ -581,6 +584,8 @@
 		} else if arg == "--soong-only" {
 			c.skipKati = true
 			c.skipKatiNinja = true
+		} else if arg == "--skip-config" {
+			c.skipConfig = true
 		} else if arg == "--skip-soong-tests" {
 			c.skipSoongTests = true
 		} else if len(arg) > 0 && arg[0] == '-' {