Unit tests for contracts

in addition to unit tests:
* in MuranoObject parent property renamed to owner
* fixed ownership of temporary method arguments
* more descriptive exceptions in contracts and related places

Change-Id: I4ee491c5428a4a64a21ccb5b1947acac386eb78f
Closes-Bug: #1337225
Partial-Bug: #1316786
Merge "Unit tests for contracts"