Improve the docstring for Swift pollsters
Improve the docstring for Swift pollsters

Currently, the docstring of all the Swift pollsters are really
unclear, confused. This patch fixes it.

Change-Id: I2f2879a2c8b60fad8083a175f8cb14beb87665e4

ityaptin/ceilometer,openstack/ceilometer,openstack/ceilometer,ityaptin/ceilometer