line_protocol: handle py2/py3 difference in _get_unicode().

Fix test_make_lines_unicode() test. _get_unicode() with flag fails
under py27 if tag contains unicode.

Author: anonymouzz

influxdb/line_protocol.py

@@ -7,7 +7,7 @@
 from numbers import Integral
 
 from dateutil.parser import parse
-from six import binary_type, text_type, integer_types
+from six import binary_type, text_type, integer_types, PY2
 
 
 def _convert_timestamp(timestamp, precision=None):
@@ -74,7 +74,10 @@ def _get_unicode(data, force=False):
     elif data is None:
         return ''
     elif force:
-        return str(data)
+        if PY2:
+            return unicode(data)
+        else:
+            return str(data)
     else:
         return data