[chiptest] Fix UTF-8 decoding error in stdout/err

Previous implementation was pron to decoding errors when test
output was a byte-string instead of correct UTF-8 text.

This commit also simplifies PIPE creation for the purpose of
collecting logs asynchronously. The PIPE object is created by
the Popen function itself, so we will hot have to worry about
bare file descriptors any more.

scripts/tests/chiptest/runner.py

@@ -13,30 +13,22 @@
 # limitations under the License.
 
 import logging
-import os
-import pty
 import re
 import subprocess
-import sys
 import threading
 
 
 class LogPipe(threading.Thread):
 
-    def __init__(self, level, capture_delegate=None, name=None):
+    def __init__(self, level, pipe, capture_delegate=None, name=None):
         """
         Setup the object with a logger and a loglevel and start the thread.
         """
         threading.Thread.__init__(self)
 
         self.daemon = False
         self.level = level
-        if sys.platform == 'darwin':
-            self.fd_read, self.fd_write = pty.openpty()
-        else:
-            self.fd_read, self.fd_write = os.pipe()
-
-        self.pipeReader = os.fdopen(self.fd_read)
+        self.pipe = pipe
         self.captured_logs = []
         self.capture_delegate = capture_delegate
         self.name = name
@@ -56,43 +48,38 @@ def FindLastMatchingLine(self, matcher):
                 return match
         return None
 
-    def fileno(self):
-        """Return the write file descriptor of the pipe."""
-        return self.fd_write
-
     def run(self):
         """Run the thread, logging everything."""
-        for line in iter(self.pipeReader.readline, ''):
+        for line in iter(self.pipe.readline, b''):
+            line = line.decode('utf-8', 'ignore')
             logging.log(self.level, line.strip('\n'))
             self.captured_logs.append(line)
             if self.capture_delegate:
                 self.capture_delegate.Log(self.name, line)
 
-        self.pipeReader.close()
-
-    def close(self):
-        """Close the write end of the pipe."""
-        os.close(self.fd_write)
-
 
 class Runner:
+
     def __init__(self, capture_delegate=None):
         self.capture_delegate = capture_delegate
 
     def RunSubprocess(self, cmd, name, wait=True, dependencies=[]):
-        outpipe = LogPipe(
-            logging.DEBUG, capture_delegate=self.capture_delegate,
-            name=name + ' OUT')
-        errpipe = LogPipe(
-            logging.INFO, capture_delegate=self.capture_delegate,
-            name=name + ' ERR')
 
         if self.capture_delegate:
             self.capture_delegate.Log(name, 'EXECUTING %r' % cmd)
 
-        s = subprocess.Popen(cmd, stdout=outpipe, stderr=errpipe)
-        outpipe.close()
-        errpipe.close()
+        s = subprocess.Popen(
+            cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+
+        outpipe = LogPipe(
+            logging.DEBUG, s.stdout,
+            capture_delegate=self.capture_delegate,
+            name=name + ' OUT')
+
+        errpipe = LogPipe(
+            logging.INFO, s.stderr,
+            capture_delegate=self.capture_delegate,
+            name=name + ' ERR')
 
         if not wait:
             return s, outpipe, errpipe