Rework pipenv

Ansible 2.5.0 currently has problems with Jinja2 expressions and vaults
so I decided to use Ansible from a source checkout of the devel branch.

I removed the old Pipfile and re-created it with Python 2 and satisfied
the dependencies from requirements.txt, then sourced Ansible:

  $ rm Pipfile*
  $ pipenv install --two -r ~/src/git/ansible/requirements.txt
  $ pipenv shell
  $ source ~/src/git/ansible/hacking/env-setup

Pipfile

@@ -4,12 +4,12 @@ verify_ssl = true
 name = "pypi"
 
 [packages]
-ansible = "*"
-ansible-lint = "*"
-pip = "*"
-setuptools = "*"
+"Jinja2" = "*"
+PyYAML = "*"
+paramiko = "*"
+cryptography = "*"
 
 [dev-packages]
 
 [requires]
-python_version = "3.6"
+python_version = "2.7"