UG edits: cli_nova_manage_instances section

- Breaking up https://review.openstack.org/#/c/89581/
- cli_nova_manage_instances and associated files

Change-Id: I301ea42b29690a67859e3ac600817792ca76afcf
Merge "UG edits: cli_nova_manage_instances section"
Remove links to old, solved bugs

The documentation includes workarounds due to bugs, which can
 be solved after some time. This patch removes references to
bugs which have been solved.

Change-Id: I4e4cb3bb70b3b9f68e995d00cc83cb8db1d19499