Tests with errors

Tests with errors

Sending incorrect values to sessiond
server and takes back error codes

for:
 subsession_add_user
 subsession_remove_user
 subsession_switch_user

Removed test_api_adduser.cpp.
Removed test_api_removeuser.cpp
Tests from theese files are moved to test_api_addremove_user.cpp

Fixed errors in libsessiond  detected by tests

subsession_add_user,
subsession_remove_user,
subsession_switch_user will not call callback if error

Validation macros partially moved to lib.h
Validation macros are more generic

Change-Id: Ide27b2cfd8ffc6d31813230f3a43bafb6079584c