[INTERNAL] P13nConditionPanel.js : making keyfield combobox not editable 
[INTERNAL] P13nConditionPanel.js : making keyfield combobox not editable 

When only a single keyfield exist in the combobox the field change to
editable false

JIRA: CPOUIFDENVER-1013
Change-Id: I2afca3e188e1eed5aabf4eb10cc1e4d7f3444cfe

cschuff/openui5,SQCLabs/openui5,SQCLabs/openui5,nzamani/openui5,cschuff/openui5,SQCLabs/openui5,cschuff/openui5,SAP/openui5,nzamani/openui5,nzamani/openui5,SAP/openui5,SAP/openui5,SAP/openui5