Source lib/neutron in boot_from_volume.sh

Without lib/neutron, boot_from_volume.sh generates the following
error:

  + _ping_check_neutron private 10.11.12.5 30
  /devstack/functions: line 356: _ping_check_neutron: command not found

Change-Id: Ib72c3f24d614570d69bf5dda35cbaf5847b1d1b9
Merge "Source lib/neutron in boot_from_volume.sh"