CLI: fix autocompletion bugs

The new complete_with_object() method in FieldAssignmentBase was calling
complete() using an object at the wrong depth level in the object hierarchy.
In the example, this meant calling complete on the Router object instead
of the RouterPort object.

Also, list filters didn't have an implemented autocomplete, because they
were using the redundant and incompete Seq class. This patch removes that
class and uses Concat in its place, which implements complete() correctly.

Fixes MN-189
Related to MN-192

Signed-off-by: Guillermo Ontanon <guillermo@midokura.jp>
CLI: fix bug in contructor parameter ordering

A new 'unsetter' parameter was introduced in SingleAttr, however some
subclasses that don't need it didn't add it to their call to the superclass.
The were sensitive to this change because they call the super class passing
arguments by ordering, not by name.

Fixed this by moving 'unsetter' to the last place in the list, which makes
sense because it's the least likely argument to be passed: only device
ports have a special-purposed 'unsetter'.

Fixes MN-192.

Signed-off-by: Guillermo Ontanon <guillermo@midokura.jp>
Merge pull request #59 from gontanon/autocomplete

Two fixes for bugs found in the v1.2 QA cycle