app/testeventdev: add common helper functions

adding common helper functions that used in test framework and
in all the test cases.

Signed-off-by: Jerin Jacob <jerin.jacob@caviumnetworks.com>
Signed-off-by: Guduri Prathyusha <gprathyusha@caviumnetworks.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>