Do not set special_service_provider on RHEL7.

RHEL7 uses systemd and should set this to undef as Fedora does.

Change-Id: Ic9a719dfff50bda85d428fba5d665d7b97d8959c
support for managing ssh keys

This change permits provisioning ssh public and private keys as part of
creating the "nova" user.  There are no changes to the default behavior
of the module.  This changes introduces three new parameters:

- nova_public_key
- nova_private_key
- nova_shell

These changes are intended to permit configuring live migration via
qemu+ssh connections to remote hypervisors.

Change-Id: Ib61f4574843a7e5ada9a08692f4488cb844c9eee
Implements: blueprint provision-ssh-keys
RHEL should have default provider

On RHEL-7 systemd is used and the default provider (service I suppose)
works on older releases too.

Change-Id: I4cb378350cb8de7f7c1ce1c3caacabbe682227da
Merge "RHEL should have default provider"
Merge "support for managing ssh keys"
Merge "Do not set special_service_provider on RHEL7."