Pass through all options with -Bbest.

Remove the union in bdev_specs and store all options if -Bbest is passed. Fixes issue #31.

Signed-off-by: Sidnei da Silva <sidnei.da.silva@canonical.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
bdev.c: don't free right before exit

Also log execlp error code if it returns.

Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>