libvirt: making set_host_enabled to be a private methods

Currently _set_host_enabled() is being used only for internal libvirt
driver purposes, which doesn't correlate to set_host_enabled in the
compute API.

_set_host_enabled in the driver is disabling and re-enabling
the compute service automatically and shouldn't be exposed to the users.

Also, adding disable_reason as an optional variable and enabled variable
to be boolean only.

Change-Id: I5fd13ef352fcbb4a1c96764a9e473cdaf7b128da
Closes-Bug: #1251803
Support setting a machine type to enable ARMv7/AArch64 guests to boot

By default the libvirt driver does not specify a machine type. On ARM systems
that results in a default type which will fail. This change provides two ways
to have Nova specify a machine type in the libvirt configuration:

1) The image can be tagged with the property "hw_machine_type=<type>"
2) If Nova detects an armv7 or aarch64 processor it will use vexpress-a15 or
   virt machine types respectively (this can be overridden with an image
   property)

Change-Id: I8aadfcf50e35a1370783ea795f80b29c1a71abff
Closes-Bug: #1261978
DocImpact
Fix break in vm_vdi_cleaner after oslo changes.

Added missing imports along with adding a call to config.parser_args as needed
to allow vm_vdi_cleaner to work against current master.

Corrected spelling error in comment.

Change-Id: I4d30d0f7f9718cb29fb8c4c18e9e6fa23f3496ef
Closes-Bug: #1279942
Update the mailmap

Change-Id: Ifa5c765cabf38173d4a7442bdeac79dd15dbb79d
Replace assertEqual(None, *) with assertIsNone in tests

Replace assertEqual(None, *) with assertIsNone in tests to have
more clear messages in case of failure.

Change-Id: I0d38a82e78fbe94657ab9a71c08422007843d179
VMware: remove unused class

The Failure class has not been used since it was added
to the code base. This was done in the commit below:-
https://code.launchpad.net/~citrix-openstack/nova/vmware-vsphere-support/+merge/53060

Change-Id: Ib4f0372f847bcbefde27c02b6ce01202482a46c0
Merge "Replace assertEqual(None, *) with assertIsNone in tests"
Merge "Update the mailmap"
Merge "Fix break in vm_vdi_cleaner after oslo changes."
Merge "VMware: remove unused class"
Merge "libvirt: making set_host_enabled to be a private methods"
Merge "Support setting a machine type to enable ARMv7/AArch64 guests to boot"