Adds zsh completion

Use nova bash-completion to add native zsh completion using built in
parameter expansion.  Nothing spectacular or new, this is mostly so that
zsh users do not need to autoload bashcompinit just to use nova.

Change-Id: I56f62f036e0c85e79197f4c7dfd25abf7eb4110a
Implements: zsh completion
CLI for disable service reason

Adds cli option to allow users to give reason
for service-disable. Also adds disabled reason
as a column in service list, so any disabled service
can be seen with reason.

A recent nova change that allows disable-log-reason
allows users to provide reason for disabling service.
This just adds the cli option for the method.

Blueprint record-reason-for-disabling-service

Change-Id: If263788c34279d6b4c568d5e0320448d2ff67a12
Clean up and make HACKING.rst point to openstack-dev/hacking

Instead of having a full local copy of HACKING Reference the OpenStack
hacking guide (openstack-dev/hacking) and remove duplicate sections.

Change-Id: Iaabc27c42d74b7441c17e63db15724f64114620b
Remove uncessary code related to nova start/stop

'nova start' and 'nova stop' actually send request with 'os-start'
and 'os-stop', instead of 'start' and 'stop'.

Change-Id: I1472e1b648dae8f3b281a113adb60421a00e5a48
Merge "CLI for disable service reason"
Merge "Adds zsh completion"
Merge "Remove uncessary code related to nova start/stop"
Merge "Clean up and make HACKING.rst point to openstack-dev/hacking"
Merge "Add AgregatesManager.get()"
Fix and enable gating on H402

End one-line docstrings with punctuation.
Change them to command style where necessary.

Change-Id: I8ff689c3a2f20d489286f80112c6dc95c97f2f31