Consider dest_file parameter for both .config and vm.args files

The `dest_file` parameter can now be supplied as well for standalone generation of `vm.args` files,
this allows generation of multiple `vm.args` type files that can be include from one another through
the `-args_file` parameter.

src/cuttlefish_escript.erl

@@ -35,7 +35,7 @@ cli_options() ->
  {help,         $h, "help",        undefined,          "Print this usage page"},
  {etc_dir,      $e, "etc_dir",     {string, "/etc"},   "etc dir"},
  {dest_dir,     $d, "dest_dir",    string,             "specifies the directory to write the config file to"},
- {dest_file,    $f, "dest_file",   {string, "app"},    "the file name to write"},
+ {dest_file,    $f, "dest_file",   string,             "the file name to write"},
  {schema_dir,   $s, "schema_dir",  string,             "a directory containing .schema files"},
  %%  one or more schema file paths
  {schema_file,  $i, "schema_file", string,             "individual schema file, will be processed in command line order, after -s"},
@@ -357,13 +357,14 @@ engage_cuttlefish(ParsedArgs) ->
                   Path -> Path
     end,
 
-    DestinationFilename = filename_maker(proplists:get_value(dest_file, ParsedArgs), "config"),
+    DestinationFilename = filename_maker(proplists:get_value(dest_file, ParsedArgs, "app"), "config"),
     Destination = filename:join(AbsPath, DestinationFilename),
 
-    DestinationVMArgsFilename = filename_maker("vm", "args"),
+    DestinationVMArgsFilename = filename_maker(proplists:get_value(dest_file, ParsedArgs, "vm"), "args"),
     DestinationVMArgs = filename:join(AbsPath, DestinationVMArgsFilename),
 
     lager:debug("Generating config in: ~p", [Destination]),
+    lager:debug("Generating vm.args in: ~p", [DestinationVMArgs]),
 
     Schema = load_schema(ParsedArgs),
     Conf = load_conf(ParsedArgs),

test/cuttlefish_escript_test.erl

@@ -114,4 +114,10 @@ silent_test() ->
                 ?assertPrinted("", [exact])
                end).
 
+vm_args_test() ->
+    ?capturing(begin
+                cuttlefish_escript:main(["--schema_file", "priv/erlang_vm.schema", "--conf_file", "test/riak.conf", "--etc_dir", "etc", "--dest_file", "vm.generated.args", "--allow_extra", "--silent"]),
+                ?assertPrinted("", [exact])
+               end).
+
 -endif.