Flip the Android GN debug bots to shared builds.

Prior to this change, we were doing static builds.
This will affect the following bots:
  - tryserver.v8:
    - v8_android_chromium_gn_dbg
  - tryserver.chromium.linux:
    - android_chromium_gn_compile_dbg
  - tryserver.blink:
    - android_blink_compile_dbg
  - chromium.webkit:
    - Android GN (dbg)

R=cjhopman@chromium.org
BUG=481714

Review URL: https://codereview.chromium.org/1108973002

Cr-Commit-Position: refs/heads/master@{#327413}

tools/mb/mb_config.pyl

@@ -10,7 +10,7 @@
   # bots all using the 'gn_release_bot' config).
   'configs': {
     'android_gn_release_bot': ['android', 'gn', 'release_bot'],
-    'android_gn_debug_bot': ['android', 'gn', 'debug_static_bot'],
+    'android_gn_debug_bot': ['android', 'gn', 'debug_bot'],
     'android_gn_release_trybot': ['android', 'gn', 'release_trybot'],
     'android_gyp_debug_bot': ['android', 'gyp', 'debug_bot'],
     'android_gyp_release_trybot': ['android', 'gyp', 'release_trybot'],