Call dotbot directly as subprocess

[etkeys]

• Changed calling execute_plugin.py to calling dotbot directly.
• Removed execute_plugin.py
• Tasks that need to be performed will be written to json conf file.
• Implemented _find_dotbot to get the path of dotbot shell launcher.
• base_directory now comes from self._context in case user gives override.
• Moved plugin collection to _collect_plugins.
• Sudo plugin will be excluded from plugin collection because it doesn't need to be loaded again.
• Changed subprocess.Popen to subprocess.check_call because we no longer need to directly manage the subprocess.
• Added additional logging to assit with debugging and general awareness.

Resolves #2 Since we are now calling dotbot directly, it manages loading of pyyaml dependency.