Move dexpreopt image selection out of dexpreopt package

Instead of passing both the module and global dexpreopt image
selection into the dexpreopt package, determine the correct
dexpreopt image in the java package.

Also stop using the boot image "location" as an input, only
track the real path, and then convert it to the "location"
that dex2oat expects when constructing the command line.

Test: m checkbuild
Change-Id: I2be2b5917e09fd57428dab27849c0153fdc75722
diff --git a/dexpreopt/config.go b/dexpreopt/config.go
index 319e36e..064992f 100644
--- a/dexpreopt/config.go
+++ b/dexpreopt/config.go
@@ -66,9 +66,9 @@
 
 	EmptyDirectory string // path to an empty directory
 
-	DefaultDexPreoptImageLocation map[string]string // default boot image location for each architecture
-	CpuVariant                    map[string]string // cpu variant for each architecture
-	InstructionSetFeatures        map[string]string // instruction set for each architecture
+	DefaultDexPreoptImage  map[string]string // default boot image location for each architecture
+	CpuVariant             map[string]string // cpu variant for each architecture
+	InstructionSetFeatures map[string]string // instruction set for each architecture
 
 	Tools Tools // paths to tools possibly used by the generated commands
 }
@@ -103,8 +103,8 @@
 	UsesLibraries         []string
 	LibraryPaths          map[string]string
 
-	Archs                  []string
-	DexPreoptImageLocation string
+	Archs           []string
+	DexPreoptImages []string
 
 	PreoptExtractedApk bool // Overrides OnlyPreoptModules