Add missing argument max_size in libvirt driver

max_size argument was added in commit 3cdfe894ab58f7b91bf7fb690fc5bc724e44066f,
but missing  in _create_ephemeral and _create_swap method, which cause
exception raised when caching ephemeral and swap disk files of the instance.

Add test for _create_ephemeral used with max_size parameter
and test _create_swap method

Change-Id: I46032ad32f317c923692b8b3d40cedd0dce06cad
Closes-Bug: 1251152
Closes-Bug: 1250032
Merge "Add missing argument max_size in libvirt driver"