ASACORE-1181 cleaner implementation of the SessionTest unit test

This change does not alter the functionality of SessionTest in any way.
It merely cleans up the implementation of the complex checks done after
each session manipulation by making use of gtest's AssertionResult
feature instead of relying on an ugly hack with a global "print"
variable.

Change-Id: Ic90fbdf8f7ea3170a848773337bd47a46abbd8ca
Signed-off-by: Meggan Ehret <meggan@qeo.org>