kernel: Add test for 4.14

nixos/tests/kernel-generic.nix

@@ -25,6 +25,7 @@ let
   }));
 in
 with pkgs; {
+  linux_4_14 = makeKernelTest "4.14" linuxPackages_4_14;
   linux_4_19 = makeKernelTest "4.19" linuxPackages_4_19;
   linux_5_4 = makeKernelTest "5.4" linuxPackages_5_4;
   linux_5_10 = makeKernelTest "5.10" linuxPackages_5_10;

pkgs/os-specific/linux/kernel/linux-4.14.nix

@@ -1,4 +1,4 @@
-{ lib, buildPackages, fetchurl, perl, buildLinux, modDirVersionArg ? null, ... } @ args:
+{ lib, buildPackages, fetchurl, perl, buildLinux, nixosTests, modDirVersionArg ? null, ... } @ args:
 
 with lib;
 
@@ -15,4 +15,6 @@ buildLinux (args // rec {
     url = "mirror://kernel/linux/kernel/v4.x/linux-${version}.tar.xz";
     sha256 = "0nw1jf6x5a990n69aw2da4s4lc1c7mnwiwcda40bl2rkmd24s1qm";
   };
+
+  kernelTests = args.kernelTests or [ nixosTests.kernel-generic.linux_4_14 ];
 } // (args.argsOverride or {}))