bridge: Show more info when method call fail

When the bridge try to run a method dynamically and the number of
arguments does not match the function definition, we get an unhelpful
TypeError. Now a more specific and verbose error is raised:

    Traceback (most recent call last):
      File "/usr/lib/python2.7/site-packages/yajsonrpc/__init__.py",
      line 480, in _serveRequest
        res = method(**params)
      File "/usr/share/vdsm/rpc/Bridge.py", line 254, in _dynamicMethod
        raise InvalidCall(fn, methodArgs, e)
    InvalidCall: Attempt to call function: <bound method
    StoragePool.disconnect of <API.StoragePool object at 0x7f77046397d0>>
    with arguments: (1, u'2440ff3d-275f-42e6-b204-7d055b26b174') error:
    disconnect() takes e xactly 4 arguments (3 given)

(Traceback lines wrapped for the commit message)

Change-Id: I9ec0a745ec65d3994e06a0b72ded9b7bbe55b1ae
Relates-to: https://bugzilla.redhat.com/1115033
Relates-to: https://bugzilla.redhat.com/1115044
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29457
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>