Use --gtest-filter-file on Site Isolation Android bot.

This was an inadvertent change not documented in
http://crrev.com/523031 and broke the test suite on this bot.

Since it's difficult to remove the --test-launcher-filter-file
argument which is currently being ignored, leave that as is for the
moment.

BUG=794749
NOTRY=true

Change-Id: Ib0bd2cb9cbfe3f7d72281369bdd1e991e1b591f6
Reviewed-on: https://chromium-review.googlesource.com/826464
Commit-Queue: Kenneth Russell <kbr@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523995}

testing/buildbot/chromium.fyi.json

@@ -6050,6 +6050,7 @@
       },
       {
         "args": [
+          "--gtest-filter-file=../../testing/buildbot/filters/site-per-process.content_browsertests.filter",
           "--site-per-process",
           "--test-launcher-filter-file=../../testing/buildbot/filters/site-per-process.content_browsertests.filter"
         ],

testing/buildbot/test_suite_exceptions.pyl

@@ -3368,6 +3368,9 @@
     'modifications': {
       # chromium.fyi
       'Site Isolation Android': {
+        'args': [
+          '--gtest-filter-file=../../testing/buildbot/filters/site-per-process.content_browsertests.filter',
+        ],
         'swarming': {
           'shards': 6,
         },