Bazel: Set slow tests to size="large"

We are seeing timeouts on the CI:

//gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/rest/change:rest_change_submit
//TIMEOUT in 305.1s

Increase the time allowed to run the tests to 900 seconds.

Change-Id: Ifa5e67439ab996df50cd498972d936813a6a2c01

gerrit-acceptance-tests/tests.bzl

@@ -20,7 +20,7 @@ def acceptance_tests(
       'acceptance',
       'slow',
     ],
-    size = "medium",
+    size = "large",
     jvm_flags = vm_args,
     **kwargs
   )

gerrit-elasticsearch/BUILD

@@ -35,7 +35,7 @@ junit_tests(
   name = 'elasticsearch_tests',
   tags = ['elastic', 'flaky'],
   srcs = glob(['src/test/java/**/*.java']),
-  size = "medium",
+  size = "large",
   deps = [
     ':elasticsearch',
     '//gerrit-extension-api:api',