Poll for replica read_only status in test

[Riddhi]

There is a time lag for the read_only system variable in the detached replica to change from true to false, causing the test to fail many times.
Make the test_slave_is_not_read_only poll unitl the value changes.

[Denis M. (dmakogon)]

Could you please provide any logs or steps to reproduce?

[Riddhi (ridhi-j-shah)]

Logs:

DetachReplica
 delete_before_detach_replica OK 0.46
 test_detach_replica OK 0.91
 test_slave_is_not_read_only FAIL

======================================================================
FAIL: proboscis.case.MethodTest (test_slave_is_not_read_only)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/share/python/trove/local/lib/python2.7/site-packages/proboscis/case.py", line 296, in testng_method_mistake_capture_func
    compatability.capture_type_error(s_func)
  File "/usr/share/python/trove/local/lib/python2.7/site-packages/proboscis/compatability/exceptions_2_6.py", line 27, in capture_type_error
    func()
  File "/usr/share/python/trove/local/lib/python2.7/site-packages/proboscis/case.py", line 350, in func
    func(test_case.state.get_state())
  File "/Cloud-Database/lib/private/trove/trove/tests/api/replication.py", line 214, in test_slave_is_not_read_only
    assert_equal(stdout, "0\n")
AssertionError: != 0

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/135398
Committed: https://git.openstack.org/cgit/openstack/trove/commit/?id=5c66bbc34b774250ea12bdca876f6789ad8b00b9
Submitter: Jenkins
Branch: master

commit 5c66bbc34b774250ea12bdca876f6789ad8b00b9
Author: <email address hidden> <email address hidden>
Date: Tue Nov 18 13:20:59 2014 -0600

    Poll for replica read_only status in test

    There is a time lag for the read_only system variable in the
    detached replica to change from true to false, causing the test
    to fail many times.Make the test_slave_is_not_read_only
    poll unitl the value changes.

    Change-Id: I6191cb7f85e18b30a16383675490a6186185ba5b
    Closes-Bug: #1393914