crush: display args on crushtool failure

crush: display args on crushtool failure

When the number of args provided to --build is not a multiple of 3,
display the arguments which do not comply.

For instance the --debug_crush 0 option is not consumed by global_init
in crushtool because, unlike most ceph tools, the arguments are not
passed to global_init. As a result --debug_crush 0 become part of the
arguments and triggers the failure.

   crushtool --debug_crush 0 --build --num_osds 320 node straw 4
   remaining args: [--debug_crush,0,node,straw,4]
   layers must be specified with 3-tuples of (name, buckettype, size)

Signed-off-by: Loic Dachary <loic@dachary.org>