[LNT] Python 3 support: read machine deletion page as text

[thopre]

Summary

Test server/ui/test_api_modify.py deletes some machines via the REST
interface and tests that the content of page displayed upon that action.
Since that content is made of text, it is compared against a string.
However by default Flask returns the content as binary data which leads
to an invalid comparison of str against byte. This commit fixes it by
requesting the content as a string from Flask using the as_text
parameter from get_data() property getter.

[thopre]

Merged into another patch (D68829)

tests/server/ui/test_api_modify.py

def test_02_delete_machine(self):
 
         resp = client.delete('api/db_default/v4/nts/machines/2',
                              headers={'AuthToken': 'wrong token'})
         self.assertEqual(resp.status_code, 401)
 
         resp = client.delete('api/db_default/v4/nts/machines/2',
                              headers={'AuthToken': 'test_token'})
         self.assertEqual(resp.status_code, 200)
-        self.assertEqual(resp.get_data(),
+        self.assertEqual(resp.get_data(as_text=True),
                          '''Deleting runs 3 5 6 7 8 9 (6/6)
 Deleted machine machine2:2
 ''')
 
         resp = client.get('api/db_default/v4/nts/machines/2')
         self.assertEqual(resp.status_code, 404)
 
         for run_id in run_ids: