Fix encoding error in report

[SLAVE] [INFO]      [exec] nuxeo-drive-client/tests/test_windows.py .sE
[SLAVE] [INFO]      [exec] =========================== short test summary info ============================
[SLAVE] [INFO]      [exec] ERROR nuxeo-drive-client/tests/test_windows.py::TestWindows::test_local_replace
[SLAVE] [INFO]      [exec] ==================================== ERRORS ====================================
[SLAVE] [INFO]      [exec] _____________ ERROR at teardown of TestWindows.test_local_replace ______________
[SLAVE] [INFO]      [exec] self = <tests.test_windows.TestWindows testMethod=test_local_replace>
[SLAVE] [INFO]      [exec]     def tearDown(self):
[SLAVE] [INFO]      [exec]         unittest.TestCase.tearDown(self)
[SLAVE] [INFO]      [exec]         if not self.tearedDown:
[SLAVE] [INFO]      [exec] >           self.tearDownApp()
[SLAVE] [INFO]      [exec] self       = <tests.test_windows.TestWindows testMethod=test_local_replace>
[SLAVE] [INFO]      [exec] nuxeo-drive-client/tests/common_unit_test.py:625: 
[SLAVE] [INFO]      [exec] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[SLAVE] [INFO]      [exec] nuxeo-drive-client/tests/common_unit_test.py:631: in tearDownApp
[SLAVE] [INFO]      [exec]     self.generate_report()
[SLAVE] [INFO]      [exec] nuxeo-drive-client/tests/common_unit_test.py:756: in generate_report
[SLAVE] [INFO]      [exec]     self.manager_1.generate_report(report_path)
[SLAVE] [INFO]      [exec] nuxeo-drive-client/nxdrive/manager.py:826: in generate_report
[SLAVE] [INFO]      [exec]     report.generate()
[SLAVE] [INFO]      [exec] nuxeo-drive-client/nxdrive/report.py:77: in generate
[SLAVE] [INFO]      [exec]     for line in self._export_logs():
[SLAVE] [INFO]      [exec] nuxeo-drive-client/nxdrive/report.py:59: in _export_logs
[SLAVE] [INFO]      [exec]     yield handler.format(record).encode('utf-8', errors='replace')\
[SLAVE] [INFO]      [exec] ../deploy-dir/.pyenv/versions/2.7.13/lib/python2.7/logging/__init__.py:734: in format
[SLAVE] [INFO]      [exec]     return fmt.format(record)
[SLAVE] [INFO]      [exec] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[SLAVE] [INFO]      [exec] self = <logging.Formatter object at 0x7f4fe7196210>
[SLAVE] [INFO]      [exec] record = <logging.LogRecord object at 0x7f4f1f68b650>
[SLAVE] [INFO]      [exec]     def format(self, record):
[SLAVE] [INFO]      [exec]         """
[SLAVE] [INFO]      [exec]             Format the specified record as text.
[SLAVE] [INFO]      [exec]             The record's attribute dictionary is used as the operand to a
[SLAVE] [INFO]      [exec]             string formatting operation which yields the returned string.
[SLAVE] [INFO]      [exec]             Before formatting the dictionary, a couple of preparatory steps
[SLAVE] [INFO]      [exec]             are carried out. The message attribute of the record is computed
[SLAVE] [INFO]      [exec]             using LogRecord.getMessage(). If the formatting string uses the
[SLAVE] [INFO]      [exec]             time (as determined by a call to usesTime(), formatTime() is
[SLAVE] [INFO]      [exec]             called to format the event time. If there is exception information,
[SLAVE] [INFO]      [exec]             it is formatted using formatException() and appended to the message.
[SLAVE] [INFO]      [exec]             """
[SLAVE] [INFO]      [exec]         record.message = record.getMessage()
[SLAVE] [INFO]      [exec]         if self.usesTime():
[SLAVE] [INFO]      [exec]             record.asctime = self.formatTime(record, self.datefmt)
[SLAVE] [INFO]      [exec]         try:
[SLAVE] [INFO]      [exec] >           s = self._fmt % record.__dict__
[SLAVE] [INFO]      [exec] E           UnicodeEncodeError: 'ascii' codec can't encode character u'\xea' in position 56: ordinal not in range(128)
[SLAVE] [INFO]      [exec] record     = <logging.LogRecord object at 0x7f4f1f68b650>
[SLAVE] [INFO]      [exec] self       = <logging.Formatter object at 0x7f4fe7196210>
[SLAVE] [INFO]      [exec] ../deploy-dir/.pyenv/versions/2.7.13/lib/python2.7/logging/__init__.py:469: UnicodeEncodeError