Make test_evacuate from compute API DRYer

test_evacute creates a context in almost every test
and sets its properties. Move that to a method to avoid extra
copy/paste.

Change-Id: Ib75575061bddf2546c46a6ef788ab85b5926ce69
Fix monkey_patch docstring bug

Modify Flags.monkey_patch to CONF.monkey_patch

Change-Id: I773a94d97d206bf78ac52de8e22d9e6db7650eb9
Closes-Bug: #1258048
VMware: fix rescue with disks are not hot-addable

Some disks, for example IDE, cannot be attached to an instance
when the instance is running.

Change-Id: I3360066ea6406564caa328ec052b9e3ca9d63dc6
Closes-Bug: #1247556
Merge "Make test_evacuate from compute API DRYer"
Merge "Fix monkey_patch docstring bug"
Merge "VMware: fix rescue with disks are not hot-addable"