Install tree command

Install tree command

The tree command is required to create index files
which is required for bucket level file listing on
AWS S3.

molecule tests fail on python3!

TASK [Create Dockerfiles from image names]
*************************************
13:55:49     failed: [localhost] (item=None) => {"censored": "the output
has been hidden due to the fact that 'no_log: true' was specified for
this result", "changed": false}
    fixed with:
+export MOLECULE_DEBUG=True

"msg": "Aborting, target uses selinux but python bindings
(libselinux-python) aren't installed!"
    fixed with:
deps = selinux

libselinux python3 bindins are missing from centos7.7
https://bugs.centos.org/view.php?id=16389
    fixed with:
-basepython = python3

WARNING: test command found but not installed in testenv
    fixed with:
whitelist_externals = which

Signed-off-by: Aric Gardner <agardner@linuxfoundation.org>
Change-Id: I66025284e0251b248cb035207d17034531709616