Description of problem:
Per the verification of bug 1438013, stripe -> raid1 conversion attempts wo enough PVs should fail with "Insufficient suitable allocatable extents for logical volume". If that is no longer the case, and instead an interim attempt to raid5_n should now be done we can adjust tests accordingly.

[root@hayes-03 ~]# lvcreate --yes  --type striped -i 10 -n stripe_takeover -L 300M raid_sanity
  Using default stripesize 64.00 KiB.
  Rounding size 300.00 MiB (75 extents) up to stripe boundary size 320.00 MiB(80 extents).
  Logical volume "stripe_takeover" created.

[root@hayes-03 ~]# lvs -a -o +devices
  LV              VG          Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert Devices                                                                                                                          
  stripe_takeover raid_sanity -wi-a----- 320.00m                                                     /dev/sdb1(0),/dev/sdc1(0),/dev/sdd1(0),/dev/sde1(0),/dev/sdf1(0),/dev/sdg1(0),/dev/sdh1(0),/dev/sdi1(0),/dev/sdj1(0),/dev/sdk1(0)

[root@hayes-03 ~]# lvconvert --yes --type raid1 raid_sanity/stripe_takeover
  Replaced LV type raid1 with possible type raid5_n.
  Repeat this command to convert to raid1 after an interim conversion has finished.
  Logical volume raid_sanity/stripe_takeover successfully converted.

[root@hayes-03 ~]# lvs -a -o +devices
  LV                          VG          Attr       LSize   Cpy%Sync Convert Devices
  stripe_takeover             raid_sanity rwi-a-r--- 320.00m 100.00           stripe_takeover_rimage_0(0),stripe_takeover_rimage_1(0),stripe_takeover_rimage_2(0),stripe_takeover_rimage_3(0),stripe_takeover_rimage_4(0),stripe_takeover_rimage_5(0),stripe_takeover_rimage_6(0),stripe_takeover_rimage_7(0),stripe_takeover_rimage_8(0),stripe_takeover_rimage_9(0),stripe_takeover_rimage_10(0)
  [stripe_takeover_rimage_0]  raid_sanity iwi-aor---  32.00m                  /dev/sdb1(0
  [stripe_takeover_rimage_1]  raid_sanity iwi-aor---  32.00m                  /dev/sdc1(0
  [stripe_takeover_rimage_10] raid_sanity iwi-aor---  32.00m                  /dev/sdl1(1
  [stripe_takeover_rimage_2]  raid_sanity iwi-aor---  32.00m                  /dev/sdd1(0)
  [stripe_takeover_rimage_3]  raid_sanity iwi-aor---  32.00m                  /dev/sde1(0)
  [stripe_takeover_rimage_4]  raid_sanity iwi-aor---  32.00m                  /dev/sdf1(0)
  [stripe_takeover_rimage_5]  raid_sanity iwi-aor---  32.00m                  /dev/sdg1(0)
  [stripe_takeover_rimage_6]  raid_sanity iwi-aor---  32.00m                  /dev/sdh1(0)
  [stripe_takeover_rimage_7]  raid_sanity iwi-aor---  32.00m                  /dev/sdi1(0)
  [stripe_takeover_rimage_8]  raid_sanity iwi-aor---  32.00m                  /dev/sdj1(0)
  [stripe_takeover_rimage_9]  raid_sanity iwi-aor---  32.00m                  /dev/sdk1(0)
  [stripe_takeover_rmeta_0]   raid_sanity ewi-aor---   4.00m                  /dev/sdb1(8)
  [stripe_takeover_rmeta_1]   raid_sanity ewi-aor---   4.00m                  /dev/sdc1(8)
  [stripe_takeover_rmeta_10]  raid_sanity ewi-aor---   4.00m                  /dev/sdl1(0)
  [stripe_takeover_rmeta_2]   raid_sanity ewi-aor---   4.00m                  /dev/sdd1(8)
  [stripe_takeover_rmeta_3]   raid_sanity ewi-aor---   4.00m                  /dev/sde1(8)
  [stripe_takeover_rmeta_4]   raid_sanity ewi-aor---   4.00m                  /dev/sdf1(8)
  [stripe_takeover_rmeta_5]   raid_sanity ewi-aor---   4.00m                  /dev/sdg1(8)
  [stripe_takeover_rmeta_6]   raid_sanity ewi-aor---   4.00m                  /dev/sdh1(8)
  [stripe_takeover_rmeta_7]   raid_sanity ewi-aor---   4.00m                  /dev/sdi1(8)
  [stripe_takeover_rmeta_8]   raid_sanity ewi-aor---   4.00m                  /dev/sdj1(8)
  [stripe_takeover_rmeta_9]   raid_sanity ewi-aor---   4.00m                  /dev/sdk1(8)

[root@hayes-03 ~]# lvconvert --yes --type raid1 raid_sanity/stripe_takeover
  Converting raid5_n LV raid_sanity/stripe_takeover to 2 stripes first.
  WARNING: Removing stripes from active logical volume raid_sanity/stripe_takeover will shrink it from 320.00 MiB to 32.00 MiB!
  THIS MAY DESTROY (PARTS OF) YOUR DATA!
  If that leaves the logical volume larger than 800 extents due to stripe rounding,
  you may want to grow the content afterwards (filesystem etc.)
  WARNING: to remove freed stripes after the conversion has finished, you have to run "lvconvert --stripes 1 raid_sanity/stripe_takeover"
  Can't remove stripes without --force option.
  Reshape request failed on LV raid_sanity/stripe_takeover.
  

Version-Release number of selected component (if applicable):
kernel-4.18.0-240.el8    BUILT: Wed Sep 23 04:46:11 CDT 2020
lvm2-2.03.09-5.el8    BUILT: Wed Aug 12 15:51:50 CDT 2020
lvm2-libs-2.03.09-5.el8    BUILT: Wed Aug 12 15:51:50 CDT 2020