flush data to disk after mkfsimage (#1052175)

Make sure the data is written before we do anything else with the disk
image. This shouldn't be needed, umount should take care of it, but it
also can't hurt.

Resolves: rhbz#1052175

src/pylorax/imgutils.py

@@ -318,6 +318,9 @@ def mkfsimage(fstype, rootdir, outfile, size=None, mkfsargs=[], mountargs="", gr
                 copytree(rootdir, mnt, preserve)
             do_grafts(graft, mnt, preserve)
 
+    # Make absolutely sure that the data has been written
+    runcmd(["sync"])
+
 # convenience functions with useful defaults
 def mkdosimg(rootdir, outfile, size=None, label="", mountargs="shortname=winnt,umask=0077", graft={}):
     mkfsimage("msdos", rootdir, outfile, size, mountargs=mountargs,