Fix bug 1572 - Reading availability-zone-hint for neutron from config

Fixes bug 1572 by reading the neutron-availability-zone-hint from VIM
plugin configuration, which is then applied at network-creation time.

Note: this patch also fixes some formatting issues that black showed.

Change-Id: Iaf152657ae31748ea6b4a123e8b0a0d9513cb692
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>