Enhancement of the Ansible Driver (sample mgmt driver)

To enhance flexibility for both users and Tacker administrators, we will add the following features to the Sample Ansible Driver:

1. A feature to specify the Ansible version in the Ansible Driver configuration file within the VNF-Package.
2. A feature to specify environment variables for ansible-playbook execution in tacker.conf.

Feature 1 is primarily intended for tenant use. When tenants include Ansible Playbooks, which have been validated in their development environment, in the VNF-Package and bring them into Tacker, they may face issues as the playbooks can only be executed with the single version of Ansible available in Tacker. To solve this, multiple versions of Ansible will be made available in Tacker's virtual environment, allowing tenants to select the desired version through the configuration file within the VNF-Package.

Feature 2 is mainly intended for Tacker administrators. Currently, if administrators want to enforce options related to ansible-playbook execution, such as specifying log storage locations or custom callback plugins, they need to modify the Ansible Driver's source code. By enabling environment variables to be specified in tacker.conf for ansible-playbook execution, administrators will be able to manage these settings flexibly and declaratively, according to the environment.