virt: get_started/bootstrap SELinux setup

Default testing for libvirt and lvsb should be done with SELinux
enabled + enforcing.  However, this expects certain file/dirrectory
contexts to be setup to standardized values.  Unless the default
contexts are also set in the local SELinux policy, changing
those directories in any way will leave them with incorrect
contexts again.  Additionally, we want to be as user-friendly
as possible, checking/setting/warning as appropriate from
get_started.

* If SELinux is disabled or not available, issue warning it
  should be enabled when possible.

* If tooling is not available, print an informative message
  on how the default contexts can be set up.

* If tooling is available, and there are no prior default
  contexts, establish them, otherwise leave the existing ones alone.

* If on-disk contexts don't match expected standardized
  values, inform the user that relabeling is needed.

* Auto-fixed a bunch of pep8 reported problems

* Avoid unnecessarily re-creating shared/data symlink
  before selinux defaults/labels are checked/set

Signed-off-by: Chris Evich <cevich@redhat.com>
virt: Improve utils_selinux comments/docstrings

Signed-off-by: Chris Evich <cevich@redhat.com>
virt: Fix comment spelling mistakes

Signed-off-by: Chris Evich <cevich@redhat.com>