pyenv: install libffi-dev

Without this package, you'll get an error similar to this:

  ModuleNotFoundError: No module named '_ctypes'

Change-Id: If1b7b66217a33c9001a20449d695cd91dfa2e3c6

roles/ensure-python/vars/Debian.yaml

@@ -2,8 +2,9 @@ python_build_depends:
   - aria2
   - gcc
   - libbz2-dev
+  - libffi-dev
   - libreadline-dev
   - libssl-dev
   - libsqlite3-dev
   - make
-  - zlib1g-dev
+  - zlib1g-dev

roles/ensure-python/vars/Gentoo.yaml

@@ -1 +1,2 @@
-python_build_depends: []
+python_build_depends:
+  - virtual/libffi

roles/ensure-python/vars/RedHat.yaml

@@ -1,8 +1,9 @@
 python_build_depends:
   - bzip2-devel
   - gcc
+  - libffi-devel
   - make
   - openssl-devel
   - readline-devel
   - sqlite-devel
-  - zlib-devel
+  - zlib-devel

roles/ensure-python/vars/Suse.yaml

@@ -2,9 +2,10 @@ python_build_depends:
   - aria2
   - gcc
   - libbz2-devel
+  - libffi-devel
   - make
   - openssl-devel
   - readline-devel
   - sqlite3-devel
   - tar
-  - zlib-devel
+  - zlib-devel