OS-356: Ignore member if marked as 'not available'

Don't load member dictionary from members.conf if
'is_available' set to false.

Change-Id: Iad080cb71d1b2ca88100f10d90fee6ece210b016
OPENSTACK-383 Member list in conditional config error

Fixes error when user sets a list of members to 'dhcp_members' or
'dns_members' option.

Change-Id: I560847d127bf630f4758cd4f09a9a6a930a21935
OPENSTACK-352 NIOS network not deleted on OS network delete

NIOS network is not deleted when user deletes Openstack network.

Change-Id: I4a9155fe5eef9d359feb9a04672cb98495d71713