Change WebRTC Android Debug builders to not build all.

This will significantly reduce the wasted bandwidth consumed
when these bots are no longer archiving 13 GB for every build.

Add a new Android Builder that will build 'all' in Release mode,
but not archive the build.

This is a prerequisite for https://chromium-review.googlesource.com/423051

BUG=657315
NOTRY=True

Review-Url: https://codereview.chromium.org/2605873002
Cr-Commit-Position: refs/heads/master@{#440843}

testing/buildbot/chromium.webrtc.fyi.json

 {
-  "Android Builder (dbg)": {
+  "Android Builder": {
     "additional_compile_targets": [
       "all"
     ]
   },
+  "Android Builder (dbg)": {
+    "additional_compile_targets": [
+      "content_browsertests"
+    ]
+  },
   "Android Builder ARM64 (dbg)": {
     "additional_compile_targets": [
-      "all"
+      "content_browsertests"
     ]
   },
   "Linux Builder": {