[JENKINS-18855] Enable proxy for AWS API endpoint

Upgrading Jenkins to 1.447 LTS since `ProxyConfiguration#noProxyHost` was introduced in 1.443.
[FIXED JENKINS-18855] Enable proxy for SSH to EC2 instance

It uses HTTP proxy defined in Plugin configuration.
SOCKS proxy is not supported.
Merge pull request #90 from ohtake/18855-proxy

[JENKINS-18855] Support HTTP Proxy