[OE-core] sstate: Fix SSTATE_DUPWHITELIST variable usage

[Richard Purdie]

We need to split this variable before using it. Otherwise a single "/"
character in the list whitelists every overlapping sysroot file which
was not the intention making the whole thing useless.

We'll start seeing warnings about overlapping files now this is working
correctly after this patch.

Signed-off-by: Richard Purdie <richard.purdie at linuxfoundation.org>
---
diff --git a/meta/classes/sstate.bbclass b/meta/classes/sstate.bbclass
index 6ccaf6d..0037ce5 100644
--- a/meta/classes/sstate.bbclass
+++ b/meta/classes/sstate.bbclass
@@ -144,7 +144,7 @@ def sstate_install(ss, d):
 
     # Check the file list for conflicts against the master manifest
     mastermanifest = d.getVar("SSTATE_MASTERMANIFEST", True)
-    whitelist = d.getVar("SSTATE_DUPWHITELIST", True)
+    whitelist = (d.getVar("SSTATE_DUPWHITELIST", True) or "").split()
     lock = bb.utils.lockfile(mastermanifest + ".lock")
     if not os.path.exists(mastermanifest):
         open(mastermanifest, "w").close()