Normalize scratchdir globally

There remain issues where relative path can screw up the transient mounts.  Normalize it to be consistent using absolute path every time.

imgutil/imgutil

@@ -1046,6 +1046,8 @@ def main():
     capturep.add_argument('node', help='Node to capture image from')
     capturep.add_argument('profilename', help='Profile name for captured image')
     args = parser.parse_args()
+    if args.scratchdir:
+        args.scratchdir = os.path.abspath(args.scratchdir)
     if not args or not args.subcommand:
         parser.print_usage()
         sys.exit(1)