python-blivet: Fix path and call to wipefs.

First of all, the path to wipefs didn't work at all, and though it is
documented, the "-f" flag only works when used as a long option ("--force").
This is probably fixed upstream in util-linux, but using the long-option will
stay compatible.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/top-level/python-packages.nix

@@ -467,6 +467,10 @@ pythonPackages = python.modules // rec {
       }' blivet/pyudev.py
       sed -i -e 's|"multipath"|"${pkgs.multipath_tools}/sbin/multipath"|' \
         blivet/devicelibs/mpath.py blivet/devices.py
+      sed -i -e '/"wipefs"/ {
+        s|wipefs|${pkgs.utillinux}/sbin/wipefs|
+        s/-f/--force/
+      }' blivet/formats/__init__.py
     '';
 
     propagatedBuildInputs = let