Bug 1482231 - Increase test chunks for geckoview-junit to avoid intermittent timeouts; r=jmaher

Increase test chunks for Android 4.3 /opt and /debug and ccov geckoview-junit.
Most chunks run in 20 to 30 minutes with this change:
https://treeherder.mozilla.org/#/jobs?repo=try&tier=1%2C2%2C3&revision=a952f0dde8b508d8f87867757d98ca2642cbd48c

Differential Revision: https://phabricator.services.mozilla.com/D21762

--HG--
extra : moz-landing-system : lando

taskcluster/ci/test/misc.yml

@@ -13,9 +13,9 @@ geckoview-junit:
             default: default
     chunks:
         by-test-platform:
-            android-em-4.3-arm7-api-16-ccov/debug: 6
-            android-em-4.3-arm7-api-16/debug: 6
-            android-em-4.3-arm7-api-16/opt: 2
+            android-em-4.3-arm7-api-16-ccov/debug: 8
+            android-em-4.3-arm7-api-16/debug: 8
+            android-em-4.3-arm7-api-16/opt: 3
             default: 1
     mozharness:
         script: android_emulator_unittest.py