Reland "luci: increase the experimental percentage to 20 from 5 for MM-x86-rel"

This reverts commit f6c32bf7.

Reason for revert: The pool is in a good shape now: http://shortn/_50OsDGj4Ll, and Pie and M CQ do not have test regression

Original change's description:
> Revert "luci: increase the experimental percentage to 20 from 5 for MM-x86-rel"
>
> This reverts commit 4f50dcad.
>
> Reason for revert: Revert to release resource for Android M CQ builder as the bot usage is high now: http://shortn/_6Egeg4knUp
>
> Original change's description:
> > luci: increase the experimental percentage to 20 from 5 for MM-x86-rel
> >
> > The builder runs a smaller test suite since crrev.com/c/2422710.
> > The GCE capacity should be able to hold more traffic.
> >
> > Bug: 997376, 1127110
> > Change-Id: I23c9bb5b55aa5f335dea3bdc1817c4793fcf9eb0
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2429249
> > Reviewed-by: Yuke Liao <liaoyuke@chromium.org>
> > Commit-Queue: Haiyang Pan <hypan@google.com>
> > Cr-Commit-Position: refs/heads/master@{#811299}
>
> TBR=liaoyuke@chromium.org,hypan@google.com
>
> Change-Id: Iddef5694a45ec74fcfd4bb478008963bde2fcf5c
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 997376
> Bug: 1127110
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2436854
> Reviewed-by: Haiyang Pan <hypan@google.com>
> Commit-Queue: Haiyang Pan <hypan@google.com>
> Cr-Commit-Position: refs/heads/master@{#811409}

TBR=liaoyuke@chromium.org,hypan@google.com

# Not skipping CQ checks because this is a reland.

Bug: 997376
Bug: 1127110
Change-Id: I33eca2c7caf5991ed82835d5f01d66daf871eec1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437700Reviewed-by: Haiyang Pan <hypan@google.com>
Commit-Queue: Haiyang Pan <hypan@google.com>
Cr-Commit-Position: refs/heads/master@{#811730}

infra/config/generated/commit-queue.cfg

@@ -239,7 +239,7 @@ config_groups {
       }
       builders {
         name: "chromium/try/android-marshmallow-x86-rel"
-        experiment_percentage: 5
+        experiment_percentage: 20
         location_regexp: ".*"
         location_regexp_exclude: ".+/[+]/docs/.+"
         location_regexp_exclude: ".+/[+]/infra/config/.+"

infra/config/generated/cq-builders.md

@@ -348,7 +348,7 @@ by CQ. These are often used to test new configurations before they are added
 as required builders.
 
 * [android-marshmallow-x86-rel](https://ci.chromium.org/p/chromium/builders/try/android-marshmallow-x86-rel) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+android-marshmallow-x86-rel)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+android-marshmallow-x86-rel))
-  * Experiment percentage: 5
+  * Experiment percentage: 20
 
 * [android-pie-arm64-rel](https://ci.chromium.org/p/chromium/builders/try/android-pie-arm64-rel) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+android-pie-arm64-rel)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+android-pie-arm64-rel))
   * Experiment percentage: 60

infra/config/subprojects/chromium/try.star

@@ -265,7 +265,7 @@ try_.chromium_android_builder(
     goma_jobs = goma.jobs.J300,
     ssd = True,
     tryjob = try_.job(
-        experiment_percentage = 5,
+        experiment_percentage = 20,
     ),
 )