always import install.yml when using local dir

[appliedprivacy]

fixes #160
solution proposed by @paulfantom

[paulfantom]

Apparently, ansible-lint don't like comparisons to empty string (E602 from https://docs.ansible.com/ansible-lint/rules/default_rules.html). I wonder if just ( node_exporter_binary_local_dir ) would work, if not let's exclude E602 in https://github.com/cloudalchemy/ansible-node-exporter/blob/master/.ansible-lint.

[appliedprivacy]

you seem to use | length > 0 in other places, ok to use it here as well?

[appliedprivacy]

The error message does not say much but I assume it fails on 2.9 due to #158.

[paulfantom]

Failure is not related to #158 (that error does not manifest itself when installing ansible via pip). This is typical molecule failure to create test instance.