Add support of http_proxy

Add possibility to use HTTP proxy for installing gem packages

Related-PROD: PROD-36623
Change-Id: Id7031f5e52c38ede08ffb50786dd39e601f31a6e
diff --git a/fluentd/agent.sls b/fluentd/agent.sls
index 78719f0..bbc3117 100644
--- a/fluentd/agent.sls
+++ b/fluentd/agent.sls
@@ -17,6 +17,9 @@
   gem.installed:
     - names: {{ plugin.get('gem') }}
     - gem_bin: {{ fluentd_agent.gem_path }}
+    {%- if fluentd_agent.get('http_proxy', None) %}
+    - proxy: {{ fluentd_agent.get('http_proxy') }}
+    {%- endif %}
     - require:
       - pkg: fluentd_packages_agent
   {%- endif %}