Fix wrong number of mirror log at allocate policy

Fix wrong number of mirror log at allocate policy

With mirror_log_fault_policy of 'remove' and mirror_image_fault_policy
of 'allocate', the log type of the mirror volume is converted from
'disk' or 'mirrored' to 'core' when all mirror legs but one in a mirror
volume broke.

Keep new_log_count as a number of valid log devices by using log_count
variable for a temporary usage in the first phase of error recovery
in _lvconvert_mirrors_repair().

Signed-off-by: Takahiro Yasui <takahiro.yasui@hds.com>
Reviewed-by: Petr Rockai <prockai@redhat.com>