Rename env variable, refactor tests

Drops the ancient rc-file convention in favor of YAMLLINT_CONFIG_FILE to
be more consistent with the rest of the documentation.

Uses the `tempfile` module's `NamedTemporaryFile` context manager to
handle the creation and cleanup of temp files (`NamedTemporaryFile` has
a `delete` option, true by default, which removes the file once it's
closed).

tests/test_cli.py

@@ -24,6 +24,7 @@ import os
 import pty
 import shutil
 import sys
+import tempfile
 import unittest
 
 from tests.common import build_temp_workspace
@@ -286,24 +287,23 @@ class CommandLineTestCase(unittest.TestCase):
         self.assertEqual(ctx.returncode, 1)
 
     def test_run_with_user_yamllintrc_config_file(self):
-        config = os.path.join(self.wd, 'fake-local-config')
-        self.addCleanup(os.remove, config)
-        self.addCleanup(os.environ.__delitem__, 'YAMLLINTRC')
-        os.environ['YAMLLINTRC'] = config
+        self.addCleanup(os.environ.__delitem__, 'YAMLLINT_CONFIG_FILE')
 
-        with open(config, 'w') as f:
+        with tempfile.NamedTemporaryFile('w') as f:
+            os.environ['YAMLLINT_CONFIG_FILE'] = f.name
             f.write('rules: {trailing-spaces: disable}')
+            f.flush()
+            with RunContext(self) as ctx:
+                cli.run((os.path.join(self.wd, 'a.yaml'), ))
+            self.assertEqual(ctx.returncode, 0)
 
-        with RunContext(self) as ctx:
-            cli.run((os.path.join(self.wd, 'a.yaml'), ))
-        self.assertEqual(ctx.returncode, 0)
-
-        with open(config, 'w') as f:
+        with tempfile.NamedTemporaryFile('w') as f:
+            os.environ['YAMLLINT_CONFIG_FILE'] = f.name
             f.write('rules: {trailing-spaces: enable}')
-
-        with RunContext(self) as ctx:
-            cli.run((os.path.join(self.wd, 'a.yaml'), ))
-        self.assertEqual(ctx.returncode, 1)
+            f.flush()
+            with RunContext(self) as ctx:
+                cli.run((os.path.join(self.wd, 'a.yaml'), ))
+            self.assertEqual(ctx.returncode, 1)
 
     def test_run_version(self):
         with RunContext(self) as ctx:

yamllint/cli.py

@@ -144,8 +144,9 @@ def run(argv=None):
 
     args = parser.parse_args(argv)
 
-    if 'YAMLLINTRC' in os.environ:
-        user_global_config = os.path.expanduser(os.environ['YAMLLINTRC'])
+    if 'YAMLLINT_CONFIG_FILE' in os.environ:
+        user_global_config = os.path.expanduser(
+            os.environ['YAMLLINT_CONFIG_FILE'])
     # User-global config is supposed to be in ~/.config/yamllint/config
     elif 'XDG_CONFIG_HOME' in os.environ:
         user_global_config = os.path.join(