912776: use cfg.get_int for proxy port

Use get_int for proxy_port config lookups where
it need to be an integeer (ie, all cases except
where it is being used to create a string)
912776: use config.get_int for server port as well

Require python-rhsm >= 1.8.6 to have the config.get_int
912776: cast port numbers from cli to int immediately
912776: fix migration test scripts to expect get_int usage
Merge pull request #520 from candlepin/alikins/912776_proxy_port_int

Alikins/912776 proxy port int