Comment 2 for bug 1573650

Reviewed: https://review.openstack.org/309455
Committed: https://git.openstack.org/cgit/openstack/rally/commit/?id=53ad2105a960805021604dd355b30cd4bddd41c4
Submitter: Jenkins
Branch: master

commit 53ad2105a960805021604dd355b30cd4bddd41c4
Author: Ihar Hrachyshka <email address hidden>
Date: Fri Apr 22 16:48:56 2016 +0200

    disable urllib3 warnings only if the library provide them

    SNIMissingWarning was introduced in urllib3 in 1.13.

    When using rally with an older version of urllib3 (f.e. as used in
    liberty, urllib3>=1.8.3), the SNIMissingWarning may be not present, in
    which case the code will crash with AttributeError.

    So first check whether the warning is known to the urllib3 library being
    used with rally before trying to disable it.

    Change-Id: Idcdc7b43a032212064c4ed2e1a69b67656bf801c
    Closes-Bug: #1573650