Fix symmetric vault password change when using password_files.

When using changing passwords, using password files, the file name was
being used as the password, and not its content. This patch fixes the
behavior to use the contents of the password file.

Tests have been added to ensure the correct behavior.

tests/vault/test_vault_symmetric.yml

@@ -295,5 +295,42 @@
     register: result
     failed_when: not result.failed or "Cannot modify password of inexistent vault" not in result.msg
 
+  - name: Ensure symmetric vault is present
+    ipavault:
+      ipaadmin_password: SomeADMINpassword
+      name: symvault
+      vault_type: symmetric
+      password: APasswordToChange
+      vault_data: Hello World.
+    register: result
+    failed_when: not result.changed or result.failed
+
+  - name: Change symmetric vault password, using password file.
+    ipavault:
+      ipaadmin_password: SomeADMINpassword
+      name: symvault
+      password: APasswordToChange
+      new_password_file: "{{ ansible_env.HOME }}/password.txt"
+      vault_type: symmetric
+    register: result
+    failed_when: not result.changed or result.failed
+
+  - name: Retrieve data from symmetric vault.
+    ipavault:
+      ipaadmin_password: SomeADMINpassword
+      name: symvault
+      password: SomeVAULTpassword
+      state: retrieved
+    register: result
+    failed_when: result.vault.data != 'Hello World.' or result.changed
+
+  - name: Ensure symmetric vault is absent
+    ipavault:
+      ipaadmin_password: SomeADMINpassword
+      name: symvault
+      state: absent
+    register: result
+    failed_when: not result.changed
+
   - name: Cleanup testing environment.
     import_tasks: env_cleanup.yml