Interfaces_file - improvements (#3328) (#3396)

* pythonific!! no camel cases, bitte

* simplified iface attributes parsing

* some improvements, passing tests

* simplified set_interface_option()

* further simplifications

* remove unreachable stmt

* pythonified a file open

* added changelog fragment

* adjustment per PR

* PR: fixed the auto- case

* PR: added testcase and chglog frag for the misleading change report

* extra line removed

* integration is not destructive

(cherry picked from commit 7aae8d5386)

Co-authored-by: Alexei Znamensky <103110+russoz@users.noreply.github.com>

tests/integration/targets/interfaces_file/tasks/main.yml

@@ -0,0 +1,33 @@
+---
+- name:
+  set_fact:
+    interfaces_testfile: '{{ output_dir }}/interfaces'
+
+- name: Copy interfaces file
+  copy:
+    src: 'files/interfaces_ff'
+    dest: '{{ interfaces_testfile }}'
+
+- name: Change IP address to 1.2.3.5
+  community.general.interfaces_file:
+    dest: "{{ interfaces_testfile }}"
+    iface: eno1
+    option: address
+    value: 1.2.3.5
+  register: ifile_1
+
+- assert:
+    that:
+    - ifile_1 is changed
+
+- name: Change IP address to 1.2.3.5 again
+  community.general.interfaces_file:
+    dest: "{{ interfaces_testfile }}"
+    iface: eno1
+    option: address
+    value: 1.2.3.5
+  register: ifile_2
+
+- assert:
+    that:
+    - ifile_2 is not changed