Investigate and fix the PLATdockertest

Docker test has following errors:
[2017-09-10 22:11:08.003750] [PLATdockertest] [STEP] 110.5: Deactivate an APP from REST and check APP status
2017-09-10 22:11:08,004 - PLATdockertest - INFO - Apps to deactivate: ['org.onosproject.proxyarp', 'org.onosproject.fwd']
2017-09-10 22:11:13,009 - PLATdockertest - INFO - user/passwd is: karaf/karaf
2017-09-10 22:11:13,009 - PLATdockertest - INFO - Sending request http://172.17.0.2:8181/onos/v1/applications/org.onosproject.proxyarp/active using DELETE method.
2017-09-10 22:11:13,062 - PLATdockertest - ERROR - ONOSbenchRest: Object not as expected
Traceback (most recent call last):
File "/home/sdn/OnosSystemTest/TestON/drivers/common/api/controller/onosrestdriver.py", line 346, in deactivateApp
app.get( 'state' ) + " state" )
TypeError: cannot concatenate 'str' and 'NoneType' objects
2017-09-10 22:11:18,068 - PLATdockertest - INFO - user/passwd is: karaf/karaf
2017-09-10 22:11:18,068 - PLATdockertest - INFO - Sending request http://172.17.0.2:8181/onos/v1/applications/org.onosproject.fwd/active using DELETE method.
2017-09-10 22:11:18,605 - PLATdockertest - ERROR - ONOSbenchRest: Object not as expected
Traceback (most recent call last):
File "/home/sdn/OnosSystemTest/TestON/drivers/common/api/controller/onosrestdriver.py", line 346, in deactivateApp
app.get( 'state' ) + " state" )
TypeError: cannot concatenate 'str' and 'NoneType' objects
2017-09-10 22:11:18,605 - PLATdockertest - DEBUG - Apps deactivation result for org.onosproject.proxyarp,org.onosproject.fwd: [None, None]
2017-09-10 22:11:18,605 - PLATdockertest - INFO - Verifying the Expected is equal to the actual or not using assert_equal
2017-09-10 22:11:18,606 - PLATdockertest - ERROR - Failed to deactivated apps correctly