Fix pip idempotence in check mode

PIP package names must be case insensitive, and must consider hyphens
and underscores to be equivalent
(https://www.python.org/dev/peps/pep-0426/#name), because of this the
module didn't work correctly in check mode. For example if the passed
package name had a different case or an underscore instead of a hyphen
(or the other way around) compared to the installed package, check mode
reported as changed, even though packages were installed. Now the module
ignores case and hyphens/underscores in package names, so check mode
works correctly.

test/integration/targets/pip/tasks/pip.yml

@@ -213,6 +213,27 @@
     that:
       - "not (q_check_mode is changed)"
 
+# Case with package name that has a different package name case and an
+# underscore instead of a hyphen
+- name: check for Junit-XML package
+  pip:
+    name: Junit-XML
+    virtualenv: "{{ output_dir }}/pipenv"
+    state: present
+
+- name: check for Junit-XML package in check_mode
+  pip:
+    name: Junit-XML
+    virtualenv: "{{ output_dir }}/pipenv"
+    state: present
+  check_mode: True
+  register: diff_case_check_mode
+
+- name: make sure Junit-XML in check_mode doesn't report changed
+  assert:
+    that:
+      - "diff_case_check_mode is not changed"
+
 # ansible#23204
 - name: ensure is a fresh virtualenv
   file: