Remove global variables from Blueprint.

The end goal of this exercise is to remove all mutable global state so
that multiple Blueprint instances can be run in the same process.

Test: Presubmit.
Change-Id: Idb34b0920f2c7d92efb9328ce8a78b7306f89571

android/config.go

@@ -68,6 +68,14 @@ func (c Config) BuildDir() string {
 	return c.buildDir
 }
 
+func (c Config) NinjaBuildDir() string {
+	return c.buildDir
+}
+
+func (c Config) SrcDir() string {
+	return c.srcDir
+}
+
 // A DeviceConfig object represents the configuration for a particular device
 // being built. For now there will only be one of these, but in the future there
 // may be multiple devices being built.