[dev-docs] Changed location of a class
[dev-docs] Changed location of a class

Changed location of BaseComputePollster class from
ceilometer/compute/__init__.py to
ceilometer/compute/pollsters/__init__.py.
Also changed ceilometer.compute.BaseComputePollster to
ceilometer.compute.pollsters.BaseComputePollster

Change-Id: I82e9bf595dca1959335ad028e7d362291e3fc1d6
Closes-Bug: #1613897

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