Better assert messages and cleanup in /tmp

TestIsLink did not clean up after itself.
Print out end of expected and actual test output more clearly
Remove unused _buffer from OutputLooper
Avoid eating too many newlines

Stripping stdout and stderr buffers removes all intentional
newlines at the end of the output as well. This reverts this
change in order to facefully return stdout and stderr.
Fix password prompt removal from stdout/err capture buffers

The capture parameter to the OutputLooper is passed by reference. The
try_again case in the OutputLooper which removes try-again strings from
the capture buffer must do the removal in-place, i.e. not replace
self.capture with another object.

Moreover, password promps have trailing newlines. These were not
removed from the capture buffers at all.
Synchronize output handler threads to avoid garbled output

Fabric is creating threads for each channel of every ssh connections. Each
of these threads is printing the outpout received from the remote but the
printing is not synchronized. This results in garbled output, for instance
if thread A is printing the "<hostname> out:" prefix while thread B is
printing the output of the remote command both printouts could be
shuffled.

Ecpected behaviour: Each thread should exculsivly print prefix + output
without being interrupted by another thread.

Synchronizing with multiprocessing locks to avoid garbled output.
Output multi-line run/sudo commands correctly
Substract prefix length from pty width in run() output
Avoid hanging output lines which might corrupt synchronized output
Prefix host specific error messages with [host] prefix
Parallel execution: Handle NetworkError exceptins in child process

Python Exceptions thrown in the child process are obviously handled
by the multiprocessing lib that is showing a traceback. The handler
of the NetworkError exception in tasks:execute was not receiving the
exception

Since we don't want to see the trace we are handling the exception
in the child process, showing an error.

For the reason of backwards compatibility env.use_exception_for['network']
is evaluated in the same manner as in tasks:execute.
Fabric tasks: Adding a summary of hosts succeeded and failed

Per task there will be summary indicating on which hosts the task
has succeeded or failed.

Meant for getting parsed by a tool connected by a pipe.
Initialize logging to avoid paramiko warnings
Avoid further unnecessary newline in output

OutputLooper and _execute try to add a newline if the command output ends
without that. OutputLooper does that in linewise mode, _execute in
non-linewise mode. A check for "not linewise" was missing from the former.
Loading Hosts from a file

A Parameter --hosts-file is introduced to load hosts from a
file. This file is a structured list of hosts:
*Each Host is listed on a line.
*Hosts may be organised in name spaces
*Name spaces are decalered in Brackets with a namespace path
	[/org1/sub1/foo/bar/baz]
*Hosts listed below a namespace declaration are members
*Hosts listed above all namespace declarations are members of a
	unnnamed root namespace

from the file only hosts that are selected will be used.

Selection of Hosts is done through the standard --hosts and
	--exclude-hosts parameters.

These have been extended to understand namespace and Hosts Selections and
Placeholders Hosts from a Namespace are selected with /name/space/path:host
Namespaces and Hosts may contain * as a placeholder for "any".

* /path/to/* Looks for hosts in the name spaces below /path/to ( eg.
	/path/to/hell /path/to/heaven.
* /na/me/space:* Selects all Hosts in the Namespace /na/me/space
Thus
* /path/to/*:bender Will select the host bender if it is in heaven,hell or both
* /path/to/heaven:bender Will select bender only if it is in heaven
* /path/to/heaven:* Will select all Hosts from heaven

As a special notation * will select all hosts just liek *:*

The selection string may contain a ! as the first character. Ths signals exclusion

A command line of fab --hosts-file /path/to/file -H *,!/path/to/heaven:* will exclude
all Hosts from the Namespace /path/to/heaven. Thus being the same as:
--hosts-file /path/to/file -H * -x /path/to/heaven:*

Exsamples:

--hosts-file /path/to/file -H host1  Will only use Host1. So it is basically useless.
--hosts-file /path/to/file -H * Will use all Hosts form the file.
--hosts-file /path/to/file -H /na/me/* Will only use Hosts from the /na/me namespace.
--hosts-file /path/to/file -H /na/me/*,host1 Will also add Host1.
--hosts-file /path/to/file -H * -x /na/me/* Will use all hosts exept thos in /na/me