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

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.