Add isolate files for Android tests

BUG=chromium:583318
TESTED=Passing runs with:
GYP_DEFINES='test_isolation_mode=prepare OS=android' webrtc/build/gyp_webrtc
ninja -C out/Release
NOTRY=True
NOPRESUBMIT=True

Review URL: https://codereview.webrtc.org/1882963003

Cr-Commit-Position: refs/heads/master@{#12397}
diff --git a/.gitignore b/.gitignore
index 30b566c..5156e51 100644
--- a/.gitignore
+++ b/.gitignore
@@ -140,6 +140,7 @@
 /tools/grit
 /tools/gyp
 /tools/isolate_driver.py
+/tools/luci-go
 /tools/mb
 /tools/memory
 /tools/protoc_wrapper