task_runner: always use run_isolated

run_isolated learned to run non-isolated commands. Use it for ordinary
commands in task_runner.

R=maruel@chromium.org
BUG=601022

Review-Url: https://codereview.chromium.org/1949613002
Cr-Mirrored-From: https://github.com/luci/luci-py
Cr-Mirrored-Commit: 5c6162e91858e17f4cfcedb50438d2e2baf5ec12
diff --git a/utils/logging_utils.py b/utils/logging_utils.py
index ce0df55..9b559f5 100644
--- a/utils/logging_utils.py
+++ b/utils/logging_utils.py
@@ -15,6 +15,7 @@
 import tempfile
 import time
 
+from utils import file_path
 
 # This works around file locking issue on Windows specifically in the case of
 # long lived child processes.
@@ -199,6 +200,7 @@
   # Setup up logging to a constant file so we can debug issues where
   # the results aren't properly sent to the result URL.
   if filename:
+    file_path.ensure_tree(os.path.dirname(os.path.abspath(unicode(filename))))
     try:
       rotating_file = NoInheritRotatingFileHandler(
           filename, maxBytes=10 * 1024 * 1024, backupCount=5,