Misc fixes - See desc

* Remove unnecessary uses of _list_from_options_callback
* Fix download tests - Bug from 6e84b21559
* Rename ExecAfterDownloadPP to ExecPP and refactor its tests
* Ensure _write_ytdl_file closes file handle on error - Potential fix for #517

yt_dlp/postprocessor/exec.py

@@ -0,0 +1,42 @@
+from __future__ import unicode_literals
+
+import subprocess
+
+from .common import PostProcessor
+from ..compat import compat_shlex_quote
+from ..utils import (
+    encodeArgument,
+    PostProcessingError,
+    variadic,
+)
+
+
+class ExecPP(PostProcessor):
+
+    def __init__(self, downloader, exec_cmd):
+        PostProcessor.__init__(self, downloader)
+        self.exec_cmd = variadic(exec_cmd)
+
+    def parse_cmd(self, cmd, info):
+        tmpl, tmpl_dict = self._downloader.prepare_outtmpl(cmd, info)
+        if tmpl_dict:  # if there are no replacements, tmpl_dict = {}
+            return self._downloader.escape_outtmpl(tmpl) % tmpl_dict
+
+        # If no replacements are found, replace {} for backard compatibility
+        if '{}' not in cmd:
+            cmd += ' {}'
+        return cmd.replace('{}', compat_shlex_quote(
+            info.get('filepath') or info['_filename']))
+
+    def run(self, info):
+        for tmpl in self.exec_cmd:
+            cmd = self.parse_cmd(tmpl, info)
+            self.to_screen('Executing command: %s' % cmd)
+            retCode = subprocess.call(encodeArgument(cmd), shell=True)
+            if retCode != 0:
+                raise PostProcessingError('Command returned error code %d' % retCode)
+        return [], info
+
+
+class ExecAfterDownloadPP(ExecPP):  # for backward compatibility
+    pass