fixup! fix more tests with wrong assumptions

Author: aduh95

test/parallel/test-fs-readfile-pipe-large.js

@@ -26,7 +26,7 @@ tmpdir.refresh();
 fs.writeFileSync(filename, dataExpected);
 
 const exec = require('child_process').exec;
-const cmd = '"$NODE" "$FILE" child < "TMP_FILE"';
+const cmd = '"$NODE" "$FILE" child < "$TMP_FILE"';
 exec(cmd, { maxBuffer: 1000000, env: {
   NODE: process.execPath,
   FILE: __filename,

test/parallel/test-fs-readfile-pipe.js

@@ -43,7 +43,7 @@ const filename = fixtures.path('readfile_pipe_test.txt');
 const dataExpected = fs.readFileSync(filename).toString();
 
 const exec = require('child_process').exec;
-const cmd = '"$NODE" "$FILE" child < "TMP_FILE"';
+const cmd = '"$NODE" "$FILE" child < "$TMP_FILE"';
 exec(cmd, {
   env: { NODE: process.execPath, FILE: __filename, TMP_FILE: filename }
 }, common.mustSucceed((stdout, stderr) => {

test/parallel/test-fs-readfilesync-pipe-large.js

@@ -23,7 +23,7 @@ tmpdir.refresh();
 fs.writeFileSync(filename, dataExpected);
 
 const exec = require('child_process').exec;
-const cmd = '"$NODE" "$FILE" child < "TMP_FILE"';
+const cmd = '"$NODE" "$FILE" child < "$TMP_FILE"';
 exec(
   cmd,
   { maxBuffer: 1000000, env: { NODE: process.execPath, FILE: __filename, TMP_FILE: filename } },