add ismount function from python Lib/posixpath.py

needed for https://github.com/ansible/ansible-modules-core/pull/2737

lib/ansible/module_utils/ismount.py

@@ -0,0 +1,90 @@
+# This code is part of Ansible, but is an independent component.
+# This particular file snippet, and this file snippet only, is based on
+# Lib/posixpath.py of cpython
+# It is licensed under the PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2
+#
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+
+import os
+
+
+def ismount(path):
+    """Test whether a path is a mount point
+    clone of os.path.ismount (from cpython Lib/posixpath.py)
+    fixed to solve https://github.com/ansible/ansible-modules-core/issues/2186
+    and workaround non-fixed http://bugs.python.org/issue2466
+    this should be rewritten as soon as python issue 2466 is fixed
+    probably check for python version and use os.path.ismount if fixed
+
+    to remove replace in this file ismount( -> os.path.ismount( and remove this
+    function"""
+
+    try:
+        s1 = os.lstat(path)
+    except OSError:
+        # the OSError should be handled with more care
+        # it could be a "permission denied" but path is still a mount
+        return False
+    else:
+        # A symlink can never be a mount point
+        if os.stat.S_ISLNK(s1.st_mode):
+            return False
+
+    parent = os.path.join(path, os.path.pardir)
+    parent = os.path.realpath(parent)
+
+    try:
+        s2 = os.lstat(parent)
+    except OSError:
+        # one should handle the returned OSError with more care to figure
+        # out whether this is still a mount
+        return False
+
+    if s1.st_dev != s2.st_dev:
+        return True     # path/.. on a different device as path
+    if s1.st_ino == s2.st_ino:
+        return True     # path/.. is the same i-node as path, i.e. path=='/'
+    return False