Rename instance_type to flavor in nova.cloudpipe

Renames 'instance_type' to 'flavor' in the nova.cloudpipe module.

The deprecated vpn_instance_type option is removed as part of
change I64548e40f so I leave it untouched here.

Part of blueprint flavor-instance-type-dedup

Change-Id: Id4fd757fabfb81ee81999e7978c924aabd0a712b
Rename instance_type to flavor in nova.utils and nova.compute.utils

Renames 'instance_type' to 'flavor' in nova.utils and nova.compute.utils
and related tests. Removes the unused fake_get method in
test_compute_utils.

Note that the nova.notifications payload isn't updated yet to store
flavor instead of instance_type so this patch still uses
payload['instance_type'] when processing the notification in
test_compute_utils.

Note that instance_type_id and the instance_type_* keys in
system_metadata are part of the data model and would require a database
migration to change, so those are not part of this patch.

Part of blueprint flavor-instance-type-dedup

Change-Id: I56815e5c8238f8e4ad4e3a2a599310da2b7f4568
Retry on deadlock in instance_metadata_update

THe instance_metadata_update() method in the sqlalchemy db API may hit a
DBDeadlock, as shown in the bug report.  Apply the necessary decorator
that will have the method retry in that case.

Change-Id: Ice3f13857ba8f4ee1d1d2dc06cef293e6d17daca
Closes-bug: #1262154
Merge "Retry on deadlock in instance_metadata_update"
Merge "Rename instance_type to flavor in nova.cloudpipe"
Merge "Rename instance_type to flavor in nova.utils and nova.compute.utils"