Description of problem:

In some flows, we verify that the flow is successful by checking
if a volume exists using Volume.getInfo verb.

When the volume does not exists (expected), vdsm logs this
confusing traceback:

2016-12-22 22:04:06,010 ERROR (jsonrpc/3) [storage.TaskManager.Task] (Task='b34e2474-46d5-4590-81ce-d7644f8419dc') Unexpected error (task:870)
Traceback (most recent call last):
  File "/usr/share/vdsm/storage/task.py", line 877, in _run
    return fn(*args, **kargs)
  File "/usr/lib/python2.7/site-packages/vdsm/logUtils.py", line 50, in wrapper
    res = f(*args, **kwargs)
  File "/usr/share/vdsm/storage/hsm.py", line 3050, in getVolumeInfo
    volUUID=volUUID).getInfo()
  File "/usr/share/vdsm/storage/sd.py", line 747, in produceVolume
    volUUID)
  File "/usr/share/vdsm/storage/fileVolume.py", line 361, in __init__
    manifest = self.manifestClass(repoPath, sdUUID, imgUUID, volUUID)
  File "/usr/share/vdsm/storage/fileVolume.py", line 61, in __init__
    volUUID)
  File "/usr/share/vdsm/storage/volume.py", line 84, in __init__
    self.validate()
  File "/usr/share/vdsm/storage/volume.py", line 107, in validate
    self.validateVolumePath()
  File "/usr/share/vdsm/storage/fileVolume.py", line 120, in validateVolumePath
    raise se.VolumeDoesNotExist(self.volUUID)
VolumeDoesNotExist: Volume does not exist: (u'877f7dd3-fba4-448c-b8e2-2ac44e368c22',)

Version-Release number of selected component (if applicable):
Any

How reproducible:
Always

Steps to Reproduce:
1. Call Volume.getInfo on non-existing volume

Actual results:
Confusing exception about expected condition.

Expected results:
Debug or info log about missing volume.

Additional info:

When a volume does not exists, getting volume information does
should return VolumeDoesNotExist error to engine, but there
is no need to log anything special in vdsm. Asking for info
about a volume is not an error in vdsm or in the client code.

However, if a volume does not exist in some other flow, this
is a fatal error that should fail loudly.

We cannot handle VolumeDoesNotExist error in a special way
and the lower level layer cannot throw another error when
a volume does not exits since the lower level layer has no
context.

One solution is to add an error wrapper that will expose
the original error code and message so it can be returned to
engine, but the top level error handler in vdsm can detect it
and avoid unhelpful logging.

A similar problem is client errors - calling with incorrect
or missing arguments. In v2v this is handled by ClientError
class.

This issue exist in other parts of the code, so we need
a generic solution that can be applied everywhere in 
a consistent way.