salt.sh: Stick to older salt-formula-neutron

salt.sh: Stick to older salt-formula-neutron

Recent changes to salt-formula-neutron, more precisely [1], broke the
compatibility with our current reclass model [2], which was not
updated to reflect the formula change.

Instead of locally patching the reclass model, install the latest
compatible version of the Neutron formula:
- 2016.12.1+201709251458.f0607d9-1xenial1;

[1] https://github.com/salt-formulas/salt-formula-neutron/commit/
    79ffa26858d682f404984175dc1ab93863a149ad
[2] https://github.com/Mirantis/reclass-system-salt-model

Change-Id: Ia1bc9de9a1543f7888688be76ff3513e6b4f062b
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>