Libvirt: default device bus for floppy block devs

Even though 'floppy' is a valid device type, libvirt driver was
not supporting it.

This patch makes the bus for floppy devices be defaulted to 'fdc' if not
specified, when running libvirt with KVM.

Also it makes the device name prefix for devices on the fdc bus default
to 'fd' so that it is possible to default device names for floppy
devices. It also makes the fdc count as valid bus for kvm/qemu
hypervisors.

This effectively adds support for the floppy devices in the libvirt
driver.

Closes-bug: #1229273

Change-Id: If030109fa16a2518a550fc0dc31341442262756c
Fixes typos in nova/compute files

blueprint fix-nova-typos

Change-Id: Iaea1c1a4154b8a8c705980e32e21d187ccb01c3c
Utilize assertIsInstance

Using assertTrue and the 'isinstance' function to test
if an object is in an instance of some class is too python2.4.
Our unit testing framework supports assertIsInstance which was created
for these types of tests. Let's use assertIsInstance for these tests.

Change-Id: Ife6ee0d96bcfa448f746378a52d0102fd44a7a28
Correct use of ConfigFilesNotFoundError

ConfigFilesNotFoundError.__init__() takes "config_files", not
"path". And pass the config value itself rather than the result
of find_file(), which is always None.

Change-Id: Ia5285d252d5636892c4fbeb9191a6c7ed4923b78
Closes-Bug: 1236176
Merge "Utilize assertIsInstance"
Merge "Libvirt: default device bus for floppy block devs"
Merge "Fixes typos in nova/compute files"
Merge "Correct use of ConfigFilesNotFoundError"