[gnome-continuous-yocto/gnomeostree-3.28-rocko: 6300/8267] wic: add Disk._prop helper

[Emmanuele Bassi <ebassi src gnome org>]

commit 0165f40cbbed9ed1f941590b0aeef3f25fadb60c
Author: Ed Bartosh <ed bartosh linux intel com>
Date:   Tue Jun 13 14:22:01 2017 +0300

    wic: add Disk._prop helper
    
    Added generic helper to use in property methods to
    access commands in a lazy manner.
    
    (From OE-Core rev: 4c1ded3ddbd04ad1640620ec1348831692a93dbe)
    
    Signed-off-by: Ed Bartosh <ed bartosh linux intel com>
    Signed-off-by: Richard Purdie <richard purdie linuxfoundation org>

 scripts/lib/wic/engine.py |   15 ++++++++++-----
 1 files changed, 10 insertions(+), 5 deletions(-)
---
diff --git a/scripts/lib/wic/engine.py b/scripts/lib/wic/engine.py
index f8f2844..e3701c4 100644
--- a/scripts/lib/wic/engine.py
+++ b/scripts/lib/wic/engine.py
@@ -267,13 +267,18 @@ class Disk:
 
         return self._partitions
 
+    def _prop(self, name):
+        """Get path to the executable in a lazy way."""
+        aname = "_%s" % name
+        if getattr(self, aname) is None:
+            setattr(self, aname, find_executable(name, self.paths))
+            if not getattr(self, aname):
+                raise WicError("Can't find executable {}".format(name))
+        return getattr(self, aname)
+
     @property
     def mdir(self):
-        if self._mdir is None:
-            self._mdir = find_executable("mdir", self.paths)
-            if not self._mdir:
-                raise WicError("Can't find executable mdir")
-        return self._mdir
+        return self._prop('mdir')
 
     def _get_part_image(self, pnum):
         if pnum not in self.partitions: