Explain why "lago ovirt stop" fails

[gbenhaim]

This is the current stack trace.
We shouldn't show it to the user. Instead, we need to explain why the operation failed,
and what needs to be done in order to run it again successfully.

@ Stopping oVirt environment: ERROR (in 0:05:25)
Error occured, aborting
Traceback (most recent call last):
File "/usr/lib/python2.7/site-packages/ovirtlago/cmd.py", line 362, in do_run
self.cli_plugins[args.ovirtverb].do_run(args)
File "/usr/lib/python2.7/site-packages/lago/plugins/cli.py", line 184, in do_run
self._do_run(**vars(args))
File "/usr/lib/python2.7/site-packages/lago/utils.py", line 501, in wrapper
return func(*args, **kwargs)
File "/usr/lib/python2.7/site-packages/lago/utils.py", line 512, in wrapper
return func(*args, prefix=prefix, **kwargs)
File "/usr/lib/python2.7/site-packages/ovirtlago/cmd.py", line 294, in do_ovirt_stop
prefix.virt_env.engine_vm().stop_all_hosts()
File "/usr/lib/python2.7/site-packages/ovirtlago/utils.py", line 148, in wrapped_func
return func(*args, **kwargs)
File "/usr/lib/python2.7/site-packages/ovirtlago/virt.py", line 446, in stop_all_hosts
testlib.assert_true_within(_host_is_maint, timeout=timeout)
File "/usr/lib/python2.7/site-packages/ovirtlago/testlib.py", line 263, in assert_true_within
assert_equals_within(func, True, timeout, allowed_exceptions)
File "/usr/lib/python2.7/site-packages/ovirtlago/testlib.py", line 237, in assert_equals_within
'%s != %s after %s seconds' % (res, value, timeout)
AssertionError: None != True after 300 seconds