Fix some incorrect description in doc.
Fix some incorrect description in doc.

doc/source/deploy/configuration.rst
* 'The Watcher system is a collection of services
that provides support to optimize your IAAS plateform. '

Fix: Typo, plateform -> platform

* Additionally, the Bare Metal service has certain
external dependencies, which are very similar to
other OpenStack services:

Fix: Bare Metal -> Watcher

* Please check your hypervisor configuration to correctly
handle instance migration.

Fix: ref of ``instance migration`` is http://docs.openstack.org/
admin-guide/compute-live-migration-usage.html

Change-Id: I00ab282a0f9ffcfddf745df1dd67418a43d70b10
Closes-Bug: #1646290

openstack/watcher,stackforge/watcher,stackforge/watcher,openstack/watcher