Btrfs-progs: detect if the disk we are formatting is a ssd

Btrfs-progs: detect if the disk we are formatting is a ssd

Patch rebased because of changes in mkfs.c but otherwise the same
as created by Josef Bacik

SSD's do not gain anything by having metadata DUP turned on.  The underlying
file system that is a part of all SSD's could easily map duplicate metadat
blocks into the same erase block which effectively eliminates the benefit of
duplicating the metadata on disk.  So detect if we are formatting a single
SSD drive and if we are do not use DUP.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Gene Czarcinski <gene@czarc.net>