LU-16971 ext2fs: make sure we have at least EXT2_FIRST_INO + 1 inodes

LU-16971 ext2fs: make sure we have at least EXT2_FIRST_INO + 1 inodes

When creating a small fs with 100 1k blocks, mke2fs fails with:

Creating filesystem with 100 1k blocks and 8 inodes

Allocating group tables: done
Writing inode tables: done
ext2fs_mkdir: Could not allocate inode in ext2 filesystem while creating /lost+found

Increase s_inodes_per_group with a step of 8 to make
sure we have at least EXT2_FIRST_INO + 1 inodes.

Change-Id: I5ac30bdadf72e17780ebef93b2e81365a8a90641
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/tools/e2fsprogs/+/51722
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>