Fix Python 3 bytes vs strings differences

Writing files was done fairly naively with our Python 2 code - this
change introduces explicit ASCII encoding when writing files.

Change-Id: I93c9fa4ba2fd8af9c9bf9424adaec602dbdca5f0

osa_toolkit/filesystem.py

@@ -193,7 +193,7 @@ def write_hostnames(save_path, hostnames_ips):
                 indent=4,
                 separators=(',', ': '),
                 sort_keys=True
-            )
+            ).encode('ascii')
         )
 
 
@@ -212,7 +212,7 @@ def _load_from_json(filename, preferred_path=None, raise_if_missing=True):
     dictionary = False
     if target_file is not False:
         with open(target_file, 'rb') as f_handle:
-            dictionary = json.loads(f_handle.read())
+            dictionary = json.loads(f_handle.read().decode('ascii'))
 
     return dictionary, target_file
 
@@ -264,7 +264,7 @@ def save_inventory(inventory_json, save_path):
     else:
         inventory_file = os.path.join(save_path, INVENTORY_FILENAME)
     with open(inventory_file, 'wb') as f:
-        f.write(inventory_json)
+        f.write(inventory_json.encode('ascii'))
         logger.info("Inventory written")
 
 

tests/test_inventory.py

@@ -570,7 +570,7 @@ class TestConfigCheckBase(unittest.TestCase):
         self.config_changed = True
         # Save new user_config_file
         with open(USER_CONFIG_FILE, 'wb') as f:
-            f.write(yaml.dump(self.user_defined_config))
+            f.write(yaml.dump(self.user_defined_config).encode('ascii'))
 
     def restore_config(self):
         # get back our initial user config file