Use HTTP_SUCCESS for checking success status code

rest_client contains HTTP_SUCCESS already for representing HTTP
success status codes and this patch replaces the status check with
it for the strict validation.

Change-Id: I70371883074addd4c76f08eced16e0b792247a5b
unskip test_integration_1

Finally the test_integration_1 test became unskipable.
* ssh a machine on neutron is not as flaky as before.
* Attaching volume to a booted instance is not flaky.
* EC2 Image bundle is working again.

Change-Id: I88dd708f1091d7d4ee1d7e03d800f7165f4936a4
TODO: Add stricter response validation.
Deduplicate negative test calls

Instead of duplicating the execute call for each negative test cases,
defining a generic way for all tests by registering a test function
dynamically on basis of the test class itself.

This is done using a class decorator (not inheritance) since it's
not possible to get the child class name on import time.

Change-Id: Ife0a8ea95ecfcac8a5f9c89babd74df0d5f884fe
Partially-implements: bp autogen-negative-tests
fix sahara base class

1. get client mamager after service available checking
2. checking cls's attribute in tearDownClass to avoid
   exceptions

Change-Id: I596284dceadcb5f0144495bd346d570c6bb35e0f
Merge "fix sahara base class"
Merge "Use HTTP_SUCCESS for checking success status code"
Merge "Deduplicate negative test calls"
Merge "unskip test_integration_1"