Change the default value for the config blazar_az_prefix
Change the default value for the config blazar_az_prefix

Current default value for the config 'blazar_az_prefix' is 'blazar:'.
However, ':' should not be included in the name of availability zones.

According to the parse_availability_zone() [1] of the API class of Nova,
there is a legacy hack to allow admins to specify hosts via an
availability zone using az:host:node. That means ':' cannot be included
in the name of an availability zone itself. But Nova accepts the
invalid name with ':'. That is reported as a bug [2].

This patch changes the default value for the config blazar_az_prefix
from 'blazar:' to 'blazar_' which does not use ':'.

[1] https://review.openstack.org/gitweb?p=openstack/nova.git;a=blob;f=nova/compute/api.py;h=46ed8e91fcc16f3755fd6a5e2e4a6d54f990cb8b;hb=HEAD#l561
[2] https://bugs.launchpad.net/nova/+bug/1695861

Change-Id: I3ad6f84c783d371d2eca2fc660bd564064df4586
Partial-Bug: #1695862
Depends-On: Iaff0b8e576dbcb56b89384ea236c3f121d4ffad1

openstack/blazar-nova,openstack/blazar-nova,stackforge/blazar-nova