PDI-3064 - junits for regression fix

	modified:   engine/test-src/org/pentaho/di/trans/steps/mapping/MappingParametersTest.java
PDI-3064 -  Mapping / Sub-transformation doesn't pick up named parameters defined in parent if they are also defined in the subtrans

fix regresion. Mapping transformation must correctly pass variables from
parent to child transformation according to 'Inherit variable' checkbox
mode.
Merge pull request #652 from prakapenka/PDI-3064v2

PDI-3064 (fix regression) Mapping / Sub-transformation doesn't pick up named parameters defined in parent if they are also defined in the subtrans