Fix citation references (Sphinx 1.6.x compatibility)

Sphinx 1.6.x gained a cross-reference check warning that caused
the build to fail in "tox -e docs" environment. Removing underscores
from the citation reference identifier ensures that the cross references
are properly detected. Similarly missing references to footnotes are
now a warning (which is upgraded to an error in the docs tox
environment) so adjust references where it makes sense and is needed.

Closes-Bug: #1695127
Change-Id: I7e55dcf910e0ba6dd85b565db8cb1ecbdd39634a

specs/mitaka/approved/expose-quiesce-unquiesce-api.rst

@@ -242,13 +242,12 @@ createImage action).
 References
 ==========
 
-.. [1] nova-specs: 'Quiesce filesystems with QEMU guest agent during image
-       snapshot':
-       https://review.openstack.org/#/c/126966/
+nova-specs: 'Quiesce filesystems with QEMU guest agent during image snapshot':
+`<https://review.openstack.org/#/c/126966/>`_
 
-.. [2] 'quiesce' and 'unquiesce' methods for libvirt driver:
-       https://blueprints.launchpad.net/nova/+spec/quiesced-image-snapshots-with-qemu-guest-agen/atomic/async
+'quiesce' and 'unquiesce' methods for libvirt driver:
+`<https://blueprints.launchpad.net/nova/+spec/quiesced-image-snapshots-with-qemu-guest-agen/atomic/async>`_
 
-.. [3] a VNF (telecom application) should, be able to restore in another site
-       for catastrophic failures happened
-       https://git.opnfv.org/cgit/multisite/tree/multisite-vnf-gr-requirement.rst
+a VNF (telecom application) should, be able to restore in another site
+for catastrophic failures happened
+`<https://git.opnfv.org/cgit/multisite/tree/multisite-vnf-gr-requirement.rst>`_

specs/mitaka/implemented/sriov-physical-function-passthrough.rst

@@ -268,7 +268,6 @@ References
 
 .. [1] https://review.openstack.org/#/c/182242/
 .. [2] https://review.openstack.org/#/c/142094/
-.. [3] https://blueprints.launchpad.net/nova/+spec/pci-passthrough-whitelist-regex
 
 History
 =======