Deletion of powervm virt driver mention

Due a change in IBM strategy, powervm has been removed, and its mention
has to be deleted from icehouse documentation.

Change-Id: I9dd9fc4a5032ac6c9094142f20e944dbda40015d
Partial-Bug: #1255422
Ceilometer endpoint doesn't need last slash

The last slash is unnecessary, it only causes redundant slash when
generate api uri, which already treated as a bug in Ceilometer.

Change-Id: I758d76e8edab6e818989bac8e05eb17c6e373546
Closes-Bug: #1269496
backport: havana
ref: https://review.openstack.org/#/c/63279/
Applied correct tag "<parameter>" in two instances.

Change-Id: I2b7e21ac5238a71ac8aaceed92f72796e9e1f418
Partial-bug: 1217503
Merge "Applied correct tag "<parameter>" in two instances."
Merge "Ceilometer endpoint doesn't need last slash"