Add tests for list_stacks and count_stacks params

There are no tests for show_deleted and show_nested
params in list_stacks and no test for show_deleted
param in count_stacks. Methods' return depends on
these params, so this patch test correct using of
these params.

Change-Id: I08a68ac7c1b1f5abeeadf8563a6b347ecee6e369
Switch to oslo.serialization

Change-Id: I09920ffdf120520112ffe1d7d7e9a3b94028019c
Merge "Add tests for list_stacks and count_stacks params"
Merge "Switch to oslo.serialization"