Rename MDA_RESERVED_SECTORS to RESERVED_SECTORS
Rename MDA_RESERVED_SECTORS to RESERVED_SECTORS

These are generic reserved sectors, and the only definite relationship
that they have to the MDA is that they come immediately after it.

Signed-off-by: mulhern <7b51bcf507bcd7afb72bf8663752c0ddbeb517f6@redhat.com>

stratis-storage/stratisd,stratis-storage/stratisd,stratis-storage/stratisd