Replace assertTrue with explicit assertIsInstance

assertIsInstance can provide useful message when test fails,
this patch replaces assertTrue(isinstance(x, y)) with
assertIsInstance(x, y).

Change-Id: Ia87b6b8d15f96ce7cf4082fc5ec599ade1d8114e
Closes-Bug: #1268480
Fix non-unique pxe driver 'instance_name'

The driver 'instance_name' property was used to determine
the image directory name for the instance's image storage.
Since there is no guarantee that the intance_name will be unique,
we will use node uuid.

Change-Id: I781424215bdeb5372ceef2d6f11737e8f003054d
Closes-Bug: #1236536
Fix non-unique tftp dir instance_uuid

The driver 'instance_uuid' property was used to determine
the tftp directory name for the instance's images.
Since there is no guarantee that the intance_uuid will be unique,
we will use node uuid.

Change-Id: Ie8422b39eb6007b833d09be1855874a82dcb17d4
Imported Translations from Transifex

Change-Id: I383c12d5d132d67606d8d9ea7004b035c952ff91
Merge "Fix non-unique pxe driver 'instance_name'"
Merge "Fix non-unique tftp dir instance_uuid"
Merge "Replace assertTrue with explicit assertIsInstance"