Description of problem:
1. Proposed title of this feature request  
Boot instance from volume with QoS


3. What is the nature and description of the request?  
Currently we can apply QoS on instances with nova flavors[1]. But, it will not get applied if user is booting instance from volume.(Either boot from image(create new volume)  or boot from volume).  I can see for cinder volumes, we need to set qos by "cinder qos-create" which we can attach it the instance. [2].

- If you have single volume type, you can mention the volume type name in "cinder.conf"
[...]
# Default volume type to use (string value)
default_volume_type = high-iops <==
[...]

With above option(default_volume_type), if you create new instance(boot from image(Create new volume)), volume will get created with volume type "high-iops" where we have set QoS.

But, if there are multiple volume types then "default_volume_type" option is not valid.

So. for cinder volumes, we need to perform 2 steps.
1. create volume with qos using cinder.
2. attach volume/boot from volume using nova.


Can we reduce it to single step ? May be by:

1.  providing option to select volume type while booting new instance from volume.
Or
2. Applying QoS defined in nova flavors to cinder volumes.

[1] https://wiki.openstack.org/wiki/InstanceResourceQuota
[2] https://paste.fedoraproject.org/412893/