Ticket #163: Refactor FSEventHandler

-Refactor log() method
Based on action name and no more EventHandler.ACTION and ACTIONING.
-Move pre()/post()/handle_pre()/handle_post() in FSLocalEventHandler.
-Add SUMMARY and factorize display() call
-Remove specific FSEventHandler where possible
Ticket #163: -t flag supports 'client'

-t option supports also 'client' as possible options.
This is the last component which was not supported in this flag.
Ticket #165: Add tests for Routers

Add tests for routers, for Start and Stop actions.
It uses the new Server actions for load/unloading modules to control
the local node configuration.
Backend: Code cleaning for BackendRegistry class.

BackendRegistry.get_selected() has been renamed selected()
Ticket #103: Identical error messages are grouped.

Proxy error messages are managed by a MsgTree which provides
features to easily group output messages.
Hostnames in message output are modified. THIS_SHINE_HOST pattern
is used for that. Hopefully it will not be used in regular output.
When displayed, THIS_SHINE_HOST pattern is replaced by the
corresponding hostnames.
Commands: Enable Summary for Mount and Umount.

Follow-up of ticket #163. Mount and Umount commands will also
display a summary table at command ends, like other target specific
commands or Status.
Ticket #12: Supplementary path for external commands is configurable.

A new option `command_path' is available in shine.conf
This option defines a specific path that could be used to launch
Lustre or ldiskfs specific commands.