Run 32 bit chrome_public_test_apk on bots with only a single device.

Release with 12 shards and debug with 20.

A release shard:
https://chromium-swarm.appspot.com/task?id=374bad1c5c50b910

A debug shard:
https://chromium-swarm.appspot.com/task?id=374bc4c487af1810

Bug: 670879
Change-Id: I3a9a0e2936269df5a8c72212cc2233803656ef3b
Reviewed-on: https://chromium-review.googlesource.com/567370Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Benjamin Pastene <bpastene@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487213}

testing/buildbot/chromium.linux.json

@@ -359,12 +359,12 @@
           ],
           "dimension_sets": [
             {
-              "android_devices": "6",
+              "android_devices": "1",
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
           ],
-          "hard_timeout": 1800,
+          "hard_timeout": 960,
           "output_links": [
             {
               "link": [
@@ -374,7 +374,8 @@
               ],
               "name": "shard #${SHARD_INDEX} logcats"
             }
-          ]
+          ],
+          "shards": 12
         },
         "test": "chrome_public_test_apk"
       },
@@ -1999,12 +2000,12 @@
           ],
           "dimension_sets": [
             {
-              "android_devices": "6",
+              "android_devices": "1",
               "device_os": "KTU84P",
               "device_type": "hammerhead"
             }
           ],
-          "hard_timeout": 2400,
+          "hard_timeout": 960,
           "output_links": [
             {
               "link": [
@@ -2014,7 +2015,8 @@
               ],
               "name": "shard #${SHARD_INDEX} logcats"
             }
-          ]
+          ],
+          "shards": 20
         },
         "test": "chrome_public_test_apk"
       },