fix #477 source bashrc and #476 intermittent tectia failures

this pull request addresses #476 and #477, by:

* supporting CLI ssh, adding a new class, and allowing you to specify in your `~/.brooklyn/brooklyn.properties`:

    brooklyn.ssh.config.tool.class=brooklyn.util.internal.ssh.cli.SshCliTool

and

* supporting configruable SSH script header, if you specify in your `~/.brooklyn/brooklyn.properties`:

    brooklyn.ssh.config.scriptHeader=#!/bin/bash -e\nif [ -f ~/.bashrc ] ; then . ~/.bashrc ; fi