lvol: Fix idempotency when size uses %VG or %PVS (#72569)

Change the behavior when using %VG or %PVS to make the `size_requested` an even
modulus of the VG's physical extents by rounding down.

This makes the usage of %VG or %PVS idempotent when the calculated
`size_requested` does not end on a physical extent boundary.

Co-authored-by: Felix Fontein <felix@fontein.de>
Co-authored-by: JuddTracy-DAS <38507478+JuddTracy-DAS@users.noreply.github.com>

changelogs/fragments/72569-lvol_percentage_fix.yml

@@ -0,0 +1,2 @@
+minor_changes:
+ - lvol - fix idempotency issue when using lvol with ``%VG`` or ``%PVS`` size options and VG is fully allocated (https://github.com/ansible-collections/community.general/pull/229).

lib/ansible/modules/system/lvol.py

@@ -477,6 +477,10 @@ def main():
                 size_requested = size_percent * this_vg['size'] / 100
             else:  # size_whole == 'FREE':
                 size_requested = size_percent * this_vg['free'] / 100
+
+            # Round down to the next lowest whole physical extent
+            size_requested -= (size_requested % this_vg['ext_size'])
+
             if '+' in size:
                 size_requested += this_lv['size']
             if this_lv['size'] < size_requested: