bitbake/cooker: Ensure matchFile returns full pathnames

We should always be passing full pathnames around within bitbake. If a file was referenced as a relative path to the current working directory, it might not get passed through the abspath call and hence the cwd would not get added as a prefix.

This change attempts to put everything through abspath and ignores failures. Any failure cases would mean the file simply wouldn't exist and then would get covered by the catchall code below.

[YOCTO #1465]

---

index 8ad4922..e036efb 100644
@@ -985,9 +985,10 @@ class BBCooker:
         """
         Find the .bb files which match the expression in 'buildfile'.
         """
-
-        if bf.startswith("/") or bf.startswith("../"):
+        try:
             bf = os.path.abspath(bf)
+        except:
+            pass
         filelist, masked = self.collect_bbfiles()
         try:
             os.stat(bf)