Fixes password behavior on Vault module.

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

tests/vault/test_vault.yml

@@ -394,6 +394,15 @@
     register: result
     failed_when: not result.changed
 
+  - name: Archive data from a file, in standard vault.
+    ipavault:
+      ipaadmin_password: SomeADMINpassword
+      name: stdvault
+      username: user01
+      in: "{{ ansible_env.HOME }}/in.txt"
+    register: result
+    failed_when: not result.changed
+
   - name: Retrieve data from standard vault.
     ipavault:
       ipaadmin_password: SomeADMINpassword