salt formulas: Pin via reclass instead of salt.sh

salt formulas: Pin via reclass instead of salt.sh

Previous commit pinned the salt-formula-package by installing a
specific version after OPNFV-specific patches were applied by
`patch.sh`. To prevent patch bypass, move the pin to reclass model.

While at it, also move salt-formula-neutron pinning to reclass to
bypass wrong minimum length of 2 for version-pinned formula pkgs.

Change-Id: I35c2773c130d79ec919685cd771311d6c11e11a8
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
(cherry picked from commit 1058c7ee35d64f38d978db2b3f840afca2facdef)