OpenStack driver documentation update

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>
Support floating IP allocation and assignation

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>
Add flag --openstack-docker-install

Boolean flag to indicate if docker have to
be installed on the machine. Useful when
docker is already installed and configured
in the OpenStack image. Default set to `true`

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>
Remove default values from usage phrase

Default value is already printed by the CLI itself

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>
Refactoring for code style consistency

Signed-off-by: Guillaume Giamarchi <guillaume.giamarchi@gmail.com>