Some little changes to prep for rolling forward the execroot change

This are random little nits that aren't dependent on changing the
directory structure, so it makes the (rather large) CL that is
coming cleaner.

--
PiperOrigin-RevId: 143690681
MOS_MIGRATED_REVID=143690681
diff --git a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
index ba48f7a..1e2e3d0 100644
--- a/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
+++ b/src/main/java/com/google/devtools/build/lib/cmdline/PackageIdentifier.java
@@ -124,7 +124,7 @@
   }
 
   public PathFragment getPathUnderExecRoot() {
-    return getSourceRoot();
+    return repository.getPathUnderExecRoot().getRelative(pkgName);
   }
 
   /**