Fix encoding of workunits under pantsd (#6505)

### Problem

On python2 under `pantsd`, workunits containing unicode are currently not encoded to bytes because the synthetic stdout that is created in that environment does not have "std" in its name. 

### Solution

Ensure that all output files in use with `PlainTextReporter` accept writes of raw bytes, and then universally encode non-`binary_type` values. Mark an integration test `@ensure_daemon` to cover this.

contrib/node/tests/python/pants_test/contrib/node/tasks/test_node_test_integration.py

@@ -6,17 +6,20 @@
 
 from builtins import range
 
-from pants_test.pants_run_integration_test import PantsRunIntegrationTest
+from pants_test.pants_run_integration_test import PantsRunIntegrationTest, ensure_daemon
 
 
 class NodeTestIntegrationTest(PantsRunIntegrationTest):
 
+  @ensure_daemon
   def test_test_simple(self):
     command = ['test',
                'contrib/node/examples/src/node/server-project:unit']
     pants_run = self.run_pants(command=command)
 
     self.assert_success(pants_run)
+    # NB: This test is marked `@ensure_daemon` to provide coverage for unicode-emitting workunits.
+    self.assertIn('✓', pants_run.stdout_data)
 
   def test_test_target_with_non_default_script_name(self):
     command = ['test',

src/python/pants/reporting/plaintext_reporter.py

@@ -9,13 +9,13 @@
 
 import six
 from colors import cyan, green, red, yellow
-from future.utils import PY2
 
 from pants.base.workunit import WorkUnit, WorkUnitLabel
 from pants.reporting.plaintext_reporter_base import PlainTextReporterBase
 from pants.reporting.report import Report
 from pants.reporting.reporter import Reporter, ReporterDestination
 from pants.util.memo import memoized_method
+from pants.util.strutil import ensure_binary
 
 
 class ToolOutputFormat(object):
@@ -94,6 +94,10 @@ class PlainTextReporter(PlainTextReporterBase):
 
   def __init__(self, run_tracker, settings):
     super(PlainTextReporter, self).__init__(run_tracker, settings)
+
+    # We eagerly validate that our output accepts raw bytes.
+    settings.outfile.write(b'')
+
     for key, value in settings.label_format.items():
       if key not in WorkUnitLabel.keys():
         self.emit('*** Got invalid key {} for --reporting-console-label-format. Expected one of {}\n'
@@ -183,16 +187,7 @@ def handle_output(self, workunit, label, s):
     self.flush()
 
   def emit(self, s, dest=ReporterDestination.OUT):
-    # In Py2, sys.stdout tries to coerce into ASCII, and will fail in coercing Unicode. So,
-    # we encode prematurely to handle unicode.
-    # In Py3, sys.stdout takes unicode, so will work normally.
-    #
-    # `self.settings.outfile` can also be `io.StringIO` instead of an std stream, in which case it only
-    # accepts unicode, so `s` does not need to be modified.
-    # TODO(python3port): Figure out if there's a better way to do this, like opening `sys.stderr` in different mode.
-    # Part of https://github.com/pantsbuild/pants/issues/6071.
-    if PY2 and 'std' in str(self.settings.outfile):
-      s = s.encode('utf-8')
+    s = ensure_binary(s)
     if dest == ReporterDestination.OUT:
       self.settings.outfile.write(s)
     elif dest == ReporterDestination.ERR:

src/python/pants/reporting/reporting.py

@@ -7,7 +7,7 @@
 import os
 import sys
 from builtins import open
-from io import StringIO
+from io import BytesIO
 
 from pants.base.workunit import WorkUnitLabel
 from pants.reporting.html_reporter import HtmlReporter
@@ -62,8 +62,8 @@ def initialize(self, run_tracker, start_time=None):
 
     # Capture initial console reporting into a buffer. We'll do something with it once
     # we know what the cmd-line flag settings are.
-    outfile = StringIO()
-    errfile = StringIO()
+    outfile = BytesIO()
+    errfile = BytesIO()
     capturing_reporter_settings = PlainTextReporter.Settings(
       outfile=outfile, errfile=errfile, log_level=Report.INFO,
       color=False, indent=True, timing=False,