Cleanup object usage in the delete path

This patch cleans up some dict-like usage of instances in the compute
api path, as well as removes a redundant direct call to fetch the
instance's system_metadata.

Related to blueprint icehouse-objects

Change-Id: I1cf89f0a46280b53d7d929ca61dde1cb3ea3cace
Add wsgiref to requirements.txt

Baremetal deploy helper (nova/cmd/baremetal_deploy_helper.py) uses
wsgiref module, so it should be in requirements.

Closes-bug: #1263480
Change-Id: Ibdd917d8065c085411a21a65e2d9ae016e265ee5
Remove duplicated test

Commit 65a870465fecdb65e3bd3a709c6ad2d06075f35d introduced
a test with a duplicate name (test_create),
shadowing the original one.
Remove the new test, since it's a subset of test_create test.

Change-Id: I2bc97ca4d086242f741c4ec5bbf4079b066f94d5
Disable libguestfs' default atexit handlers.

These aren't safe for multi-threaded applications, per the bug
report from Daniel Berrange.

Closes-bug: #1261475

Change-Id: I4cc5eaded2e21f1b2cd55615242a27b9773f0b42
Merge "Disable libguestfs' default atexit handlers."
Merge "Remove duplicated test"
Merge "Add wsgiref to requirements.txt"
Merge "Cleanup object usage in the delete path"