dmtcp: stay with python2

pkgs/os-specific/linux/dmtcp/default.nix

@@ -1,4 +1,6 @@
-{ lib, stdenv, fetchFromGitHub, bash, perl, python }:
+{ lib, stdenv, fetchFromGitHub, bash, perl, python2 }:
+
+# There are fixes for python3 compatibility on master
 
 stdenv.mkDerivation rec {
   pname = "dmtcp";
@@ -28,7 +30,7 @@ stdenv.mkDerivation rec {
     substituteInPlace test/autotest.py \
       --replace /bin/bash ${bash}/bin/bash \
       --replace /usr/bin/perl ${perl}/bin/perl \
-      --replace /usr/bin/python ${python}/bin/python \
+      --replace /usr/bin/python ${python2}/bin/python \
       --replace "os.environ['USER']" "\"nixbld1\"" \
       --replace "os.getenv('USER')" "\"nixbld1\""
   '';