imsm: write bad block log on metadata sync

imsm: write bad block log on metadata sync

Pre-allocate memory for largest possible bad block section when monitor
is being opened to avoid a need for memory allocation on metadata sync.

If memory for a structure has been allocated in mpb buffer but it hasn't
been used yet, it will be taken by next buffer grow, leading to
insufficient memory on metadata flush. Start tracking such memory and
take it into calculation when growing a buffer. Also assert has been
added to debug mode to warn when more metadata has been written than
memory allocated.

Signed-off-by: Tomasz Majchrzak <tomasz.majchrzak@intel.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>