Add http proxy support to outgoing notifcations

[imranh2]

Add proxy support for outgoing notifications by looking at system properties.

Issue: #22

Description of changes: Simply call useSystemProperties() which then finds and uses properties such as http.proxyHost, http.proxyPort, https.proxyHost...

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[vamshin]

Thanks for adding this support.

Verified existing tests pass and able to send Chime notifications

[lucaswin-amzn]

LGTM!

[tomerilp]

Hi,
Is there any documentation on how to configure Slack notification with those proxy parameters?
Where exactly should I configure the proxy?

Thanks,

[imranh2]

@tomerilp,

Always multiple ways to set proxy environment variables, but whatever suits you you

I ended up setting it system wide for java /etc/java-8-openjdk/net.properties as we isolate the entire node to one role and can track every outgoing http request.

[tomerilp]

@tomerilp,

Always multiple ways to set proxy environment variables, but whatever suits you you

I ended up setting it system wide for java /etc/java-8-openjdk/net.properties as we isolate the entire node to one role and can track every outgoing http request.

I managed to make it work by adding ES_JAVA_OPTS="-Dhttps.proxyHost=proxy.domain.com -Dhttps.proxyPort=8080" to /etc/sysconfig/elasticsearch
I wonder if it possible to apply these settings only on the plugin scope so it won't affect the entire elasticsearch.

Thanks,