wic/engine: Fix missing parted autobuilder failures

OE-Core rev: a88bcbae850a2e6d182291d3f8e167aabdbe4842 broke the ability
to find parted as it may be in sbin which is not in PATH for some users
on some distros.

Iterate on the original patch to fix this and also fix the original problem.

(From OE-Core rev: af3803e5189d7814f9dbd238fb6dab200f351e1a)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/engine.py

@@ -244,15 +244,17 @@ class Disk:
         self._psector_size = None
         self._ptable_format = None
 
+        # find parted
         # read paths from $PATH environment variable
         # if it fails, use hardcoded paths
+        pathlist = "/bin:/usr/bin:/usr/sbin:/sbin/"
         try:
-            self.paths = os.environ['PATH']
+            self.paths = os.environ['PATH'] + ":" + pathlist
         except KeyError:
-            self.paths = "/bin:/usr/bin:/usr/sbin:/sbin/"
+            self.paths = pathlist
 
         if native_sysroot:
-            for path in self.paths.split(':'):
+            for path in pathlist.split(':'):
                 self.paths = "%s%s:%s" % (native_sysroot, path, self.paths)
 
         self.parted = find_executable("parted", self.paths)