Correct the instance migration link
Correct the instance migration link

1. Update the instance migration link
2. remove the unnecessary install-guide link

configure and install Ceilometer by
https://docs.openstack.org/ceilometer/latest is enough
remove the other link.

Change-Id: I2bf408de1023750a3d1f2c9e25293649d99ac428

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