Add mock package to test env
Add mock package to test env

mock is required for py 2.7
mock is unittest.mock for py >= 3.3

FrancescAlted/PyTables,avalentino/PyTables,avalentino/PyTables,PyTables/PyTables,FrancescAlted/PyTables,PyTables/PyTables,FrancescAlted/PyTables,PyTables/PyTables,avalentino/PyTables