Use Opensmpp simulator for test utils

Currently, JSmpp is used in test utils to ensure that SMS are received correctly.
However, message decoding is done manually (JSmpp doesn't provide the algorithm to decode messages).

We should provide usage of Opensmpp simulator in tests to be sure to be compliant with SMSC servers. See https://github.com/OpenSmpp/opensmpp/blob/master/sim/src/main/java/org/smpp/smscsim/Simulator.java