Add ability to change client_body_buffer_size parameter value

Related: PROD-28629

Change-Id: I1862fda645bf8a79aa7d0364d8fe659568c4bfa5
(cherry picked from commit 9da2838ee21111176f0f9ede29d99d16d1dc61eb)
diff --git a/tests/pillar/proxy_with_ssl.sls b/tests/pillar/proxy_with_ssl.sls
index 824fa07..e1d0a8d 100644
--- a/tests/pillar/proxy_with_ssl.sls
+++ b/tests/pillar/proxy_with_ssl.sls
@@ -251,6 +251,7 @@
             port: 80
             protocol: http
             size: 10000m
+            buffer_size: 20m
             timeout: 43200
             websocket: true
             request_buffer: false