[LNT] Python 3 support: import LNT report as text

[thopre]

Summary

As per LNT documentation, all fields in the JSON that is a LNT report
file format are strings. Yet, the code responsible for adding a new ru
in LNT database reads the Flask data property holding the corresponding
LNT report file format which default to returning binary data. The code
then fail when invoking lnt.util.ImportData.import_from_string due to
using methods related to strings. This commit changes the access to the
data to using the property's getter with the as_text parameter set to
True, thereby requesting from Flask to return the data as a string.

[thopre]

Merged into another patch

lnt/server/ui/api.py

class Runs(Resource):
     method_decorators = [in_db]
 
     @staticmethod
     @requires_auth_token
     def post():
         """Add a new run into the lnt database"""
         session = request.session
         db = request.get_db()
-        data = request.data
+        data = request.get_data(as_text=True)
         select_machine = request.values.get('select_machine', 'match')
         merge = request.values.get('merge', None)
         result = lnt.util.ImportData.import_from_string(
             current_app.old_config, g.db_name, db, session, g.testsuite_name,
             data, select_machine=select_machine, merge_run=merge)
 
         error = result['error']
         if error is not None: