Added chef without version to Gemfile again

(cherry picked from commit fcc77bb103f6ea0f5e3ccd688c09d77b992b2a21)
Merge pull request #973 from vuntz/release/stoney/master

Improve comment about new role_constraints
Merge pull request #972 from tboerger/feature/stoney/gemfile-chef

[stoney] Added chef without version to Gemfile again
Must specify the version being used for the activesupport gem.
If the version is not specificed it tries the newest which we
can not support on Roxy due to the ruby version in use.

2.3.17 is what is available on the admin server.

Signed-off-by: JuanJose 'JJ' Galvez <jj.galvez@inktank.com>
(cherry picked from commit 09f9d7f6b55812d3e157b57ba193888af57f41ca)

Conflicts:
	chef/cookbooks/bluepill/recipes/default.rb
A new validation check:

* validate_count_as_odd_for_role
  As the name describes we want to check that we have an odd number
  of nodes used in a role.

Signed-off-by: JuanJose 'JJ' Galvez <jj.galvez@inktank.com>
(cherry picked from commit 82bab608043244ff6942ac7483165d5bbaf88a50)
Add proposal validation based on constraints

(cherry picked from commit 90e0d832c775de0cbbc0df5eba565543fc4e1cb1)
Merge pull request #975 from vuntz/roxy-sync

Sync with patches that went in roxy
Fixed the new constraints instance accessor

(cherry picked from commit 565e3f4ac93dddec518e88b0469237685dd10470)