Attempt to run Circle CI tests in Docker containers with Android.

This is potentially a big change, though it should (with any luck) make
tests faster, and allow us to better test Cordova functionality (at least
as far as Android is concerned). For example, if this works, we won't have
to mark the "cordova builds with server options" self-test "slow" again,
which would (re)disable it during Circle CI test runs.

cc @abernix @hwillson

.circleci/config.yml

@@ -21,9 +21,12 @@ run_env_change: &run_env_change
     sudo mkdir -p /tmp/results/junit
     sudo chmod -R a+rwx /tmp/results/
 
+    # The commands below don't work in Docker images, but might be worth
+    # reenabling if we switch back to machine:true instead of Docker.
+
     # Set the pattern for core dumps, so we can find them.
-    echo kernel.core_pattern="/tmp/core_dumps/core.%e.%p.%h.%t" | \
-        sudo tee -a /etc/sysctl.conf
+    # echo kernel.core_pattern="/tmp/core_dumps/core.%e.%p.%h.%t" | \
+    #     sudo tee -a /etc/sysctl.conf
 
     # Note that since every "run" command starts its own shell, and I wasn't
     # able to set this at a system wide level for all users, it's necessary to
@@ -31,11 +34,11 @@ run_env_change: &run_env_change
     # output a core dump.
 
     # Raise inotify user watches up higher.
-    echo fs.inotify.max_user_watches=524288 | \
-        sudo tee -a /etc/sysctl.conf
+    # echo fs.inotify.max_user_watches=524288 | \
+    #     sudo tee -a /etc/sysctl.conf
 
     # Reload sysctl so these are in effect.
-    sudo sysctl -p
+    # sudo sysctl -p
 
 # A reusable "run" snippet which enables the continued logging of memoryusage
 # to a file on disk which can be saved to build artifacts for later analysis.
@@ -65,7 +68,8 @@ run_save_node_bin: &run_save_node_bin
 # This environment is set to every job (and the initial build).
 build_machine_environment: &build_machine_environment
   # Specify that we want an actual machine (ala Circle 1.0), not a Docker image.
-  machine: true
+  docker:
+    - image: circleci/android:api-26-node8-alpha
   environment:
     # This multiplier scales the waitSecs for selftests.
     TIMEOUT_SCALE_FACTOR: 8