atest shard list
Id   Host                                         Labels
185  chromeos-server125.hot.corp.google.com       board:swanky, board:stout
189  chromeos-server134.hot.corp.google.com       board:expresso, board:daisy_spring, board:peppy
194  chromeos-server126.hot.corp.google.com       board:ninja, board:parrot
197  chromeos-server155.cbf.corp.google.com       board:falco_li, board:whirlwind, board:storm, board:earth, board:eureka, board:glados
199  chromeos-server129.hot.corp.google.com       board:mccloud, board:monroe
209  chromeos-skunk-2.mtv.corp.google.com         board:orco
210  chromeos-skunk-3.mtv.corp.google.com         board:leon
211  chromeos-skunk-4.mtv.corp.google.com         board:coral, board:banjo
212  chromeos-skunk-5.mtv.corp.google.com         board:sentry, board:lumpy
213  chromeos-skunk-1.mtv.corp.google.com         board:nyan_big
221  chromeos-server-tester1.mtv.corp.google.com  board:cyan, board:hana
222  chromeos-server-tester2.mtv.corp.google.com  board:setzer, board:bob
223  cros-full-0001.mtv.corp.google.com           board:gnawty, board:auron_paine, board:reks
224  cros-full-0002.mtv.corp.google.com           board:winky, board:sumo, board:parrot_ivb
225  cros-full-0003.mtv.corp.google.com           board:enguarde, board:tricky, board:heli, board:relm, board:edgar
226  cros-full-0004.mtv.corp.google.com           board:eve, board:veyron_jaq, board:falco
227  cros-full-0005.mtv.corp.google.com           board:caroline, board:veyron_speedy, board:stumpy
228  cros-full-0006.mtv.corp.google.com           board:terra, board:veyron_jerry, board:daisy
229  cros-full-0007.mtv.corp.google.com           board:kevin, board:snappy, board:daisy_skate
230  cros-full-0008.mtv.corp.google.com           board:celes, board:veyron_fievel, board:wolf
231  cros-full-0009.mtv.corp.google.com           board:lars, board:veyron_tiger, board:link
232  cros-full-0010.mtv.corp.google.com           board:cave, board:veyron_minnie, board:nyan_kitty
233  cros-full-0011.mtv.corp.google.com           board:veyron_mighty, board:peach_pit
234  cros-full-0012.mtv.corp.google.com           board:asuka, board:veyron_rialto, board:butterfly
235  cros-full-0013.mtv.corp.google.com           board:chell, board:veyron_mickey, board:guado, board:guado_moblab
236  cros-full-0014.mtv.corp.google.com           board:auron_yuna, board:tidus
237  cros-full-0015.mtv.corp.google.com           board:reef, board:elm
238  cros-full-0016.mtv.corp.google.com           board:pyro, board:quawks
239  cros-full-0017.mtv.corp.google.com           board:ultima, board:squawks
240  cros-full-0018.mtv.corp.google.com           board:gale
241  cros-full-0019.mtv.corp.google.com           board:soraka, board:panther, board:wizpig, board:sand
242  cros-full-0020.mtv.corp.google.com           board:clapper, board:poppy, board:kefka
243  cros-full-0021.mtv.corp.google.com           board:kip, board:nyan_blaze
244  cros-full-0022.mtv.corp.google.com           board:rikku, board:zako
245  cros-full-0023.mtv.corp.google.com           board:gandof, board:candy, board:banon
246  cros-full-0024.mtv.corp.google.com           board:lulu
247  cros-full-0025.mtv.corp.google.com           board:buddy, board:glimmer
248  cros-full-0039.mtv.corp.google.com           board:samus
249  cros-full-0040.mtv.corp.google.com           


40 is empty.

$ atest shard add_boards -l board:fizz  cros-full-0040.mtv.corp.google.com
Added boards for shards: 
	'board:fizz', 'cros-full-0040.mtv.corp.google.com'

I'm looking to backfill a new spare shard now.

I'm declaring victory here.  Follow up work is in bug 848406.