teuthology/beanstalk: workaround yaml load deprecation

teuthology/beanstalk: workaround yaml load deprecation

There is a deprecation error when beanstalk parser called:

  YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe

Since beanstalkc3 does not want to apply a fix for that
we can override yaml parser to suppress the error message
from the log.

Fixes: https://tracker.ceph.com/issues/44225
Signed-off-by: Kyr Shatskyy <kyrylo.shatskyy@suse.com>