Default the proxy_scheme config setting to "http"

[jtduffy]

The proxy_scheme config setting is currently defaulted to null. This is causing problems when proxy settings are supplied to the JFRDaemon component. This will change will default the setting to http.

Note that this won't effect the proxy settings of the agent itself, since is defaulted to http in the underlying Apache HttpHost instance if the scheme is null.

[workato-integration]

https://new-relic.atlassian.net/browse/NR-363828