Fix indentation in install-guide
Fix indentation in install-guide

* Fix indentation in create magnum's directories.

* Indentation in prerequisites for db privileges should be at
  the same level as db creation.

  See:
  openstack/openstack-manuals/doc/install-guide/source/nova-controller-install.rst
  openstack/openstack-manuals/doc/install-guide/source/glance-install.rst

  Fix in installguide-cookiecutter:
  https://review.openstack.org/#/c/325640/

Change-Id: Icecd5ede7db8982ce76e857df1042a896e293655

ArchiFleKs/magnum,ArchiFleKs/magnum,openstack/magnum,openstack/magnum