doc: Additional fixes to the SR-IOV doc
doc: Additional fixes to the SR-IOV doc

- Add steps to ensure physnets VLAN ranges are configured, if necessary
- Add steps to ensure a network using the given physnet is configured
- Update nova scheduler options, which have been moved since Ocata
  (nova 15.0.0) [1]
- Update nova PCI options, which have been moved since Ocata (nova
  15.0.0) [2]
- Simply some commands
- Some typo/grammar fixes

[1] https://github.com/openstack/nova/commit/7d0381c91a6
[2] https://github.com/openstack/nova/commit/4e5ed1c4891

Change-Id: I45fdc8e40121698bf144d0e0a65537edda2c805d
Signed-off-by: Stephen Finucane <492121341a95b3c3aab646bed44634f739dd019b@redhat.com>
Closes-Bug: #1788900

mahak/neutron,mahak/neutron,openstack/neutron,openstack/neutron,noironetworks/neutron,openstack/neutron,noironetworks/neutron,mahak/neutron