Prevent create IMSM volume with size smaller than 1M or chunk

Prevent create IMSM volume with size smaller than 1M or chunk

Block creation of the imsm volume when given size is smaller than 1M and
print appropriate message.

Commit b53bfba6119d3f6f56eb9e10e5a59da6901af159
(imsm: use rounded size for metadata initialization) introduces issue with
rounding volume sizes smaller than 1M to 0. There is an inconsistency when
size smaller than 1M was given depends of what we give as target device:
1) When block devices was given created volume has maximum available size.
2) When container symlink was given created volume has size 0. Additionally
it causes below call trace:

[69587.891556] WARNING: CPU: 28 PID: 22485 at ../drivers/md/md.c:7582 md_seq_show+0x764/0x770 [md_mod]
[69588.066405] Call Trace:
[69588.066409]  seq_read+0x336/0x430
[69588.066411]  proc_reg_read+0x40/0x70
[69588.066412]  __vfs_read+0x26/0x140
[69588.066414]  vfs_read+0x89/0x130
[69588.066415]  SyS_read+0x42/0x90
[69588.066417]  do_syscall_64+0x74/0x140
[69588.066419]  entry_SYSCALL_64_after_hwframe+0x3d/0xa2

Signed-off-by: Roman Sobanski <roman.sobanski@intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>