Allows changing passwords of symmetric waults, using a new variable
`new_password` (or the file-base version, `new_password_file`). The
old password must be passed using the `password` or `password_file`
variables that also received new aliases `old_password` and
`old_password_file`, respectively.
Tests were modyfied to reflect the changes.
This patch fixes handling of password and public_key files, parameter
validation depending on vault type, usage of `salt` attribute and data
retrieval.
Tests were updated to reflect the changes.
New example playbooks are added:
playbooks/vault/vault-is-present-with-password-file.yml
playbooks/vault/vault-is-present-with-public-key-file.yml
playbooks/vault/retrive-data-asymmetric-vault.yml
playbooks/vault/retrive-data-symmetric-vault.yml
