Increase linux-goma-rbe-staging-rel to 100%

Previously this was dropped to 10% due to infra failures.
See http://crrev.com/c/1361583

We have since added the builder to a no-alert blacklist.
See comment at http://crbug.com/911187#c13

Bug: 911187
Change-Id: I616dc30869649087b083fc7f8c84157d07e51501
Reviewed-on: https://chromium-review.googlesource.com/c/1370238
Reviewed-by: Shinya Kawanaka <shinyak@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Sergey Berezin <sergeyberezin@chromium.org>
Commit-Queue: Simon Que <sque@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615771}

docs/infra/cq_builders.md

@@ -261,7 +261,7 @@ as required builders.
 
   https://crbug.com/855319
 
-  * Experimental percentage: 10
+  * Experimental percentage: 100
 
 * [win7_chromium_rel_loc_exp](https://ci.chromium.org/p/chromium/builders/luci.chromium.try/win7_chromium_rel_loc_exp) ([`cq.cfg` entry](https://cs.chromium.org/search/?q=package:%5Echromium$+file:cq.cfg+win7_chromium_rel_loc_exp)) ([matching builders](https://cs.chromium.org/search/?q=file:trybots.py+win7_chromium_rel_loc_exp))
 

infra/config/branch/cq.cfg

@@ -238,7 +238,7 @@ verifiers {
       # https://crbug.com/855319
       builders {
         name: "linux-goma-rbe-staging-rel"
-        experiment_percentage: 10
+        experiment_percentage: 100
       }
       builders {
         name: "win7_chromium_rel_loc_exp"