doc: fix the link for the evacuate cli
doc: fix the link for the evacuate cli

This was broken during the openstack admin guide docs migration
in pike.

Change-Id: Ibb886657ed97f3e6462ceef0002ef3fe1aec767d
Closes-Bug: #1748327

mikalstill/nova,klmitch/nova,openstack/nova,openstack/nova,rahulunair/nova,mikalstill/nova,rahulunair/nova,openstack/nova,mahak/nova,klmitch/nova,mikalstill/nova,gooddata/openstack-nova,phenoxim/nova,mahak/nova,rahulunair/nova,mahak/nova,gooddata/openstack-nova,klmitch/nova,klmitch/nova,phenoxim/nova,gooddata/openstack-nova,gooddata/openstack-nova