Provider should properly failed when ansible-playbook executable is not installed

[abikouo]

This Pull requests check the executable prior running the ansible-playbook command. Fixes #35

[patchback[bot]]

Backport to stable-1: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-1/34b158a5ee310ee08432b098aa4ab01aa729fc07/pr-106

Backported as https://github.com/ansible/terraform-provider-ansible/pull/115

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