userspace/tools: replace wrs_shm_wait with wrs_shm_get_and_check in wr_mon

wrs_shm_wait is not save, change is needed.
Additionally use wrs-msg for erorr reporting:
--add msg init function
--replace "fprintf(stderr," with pr_error

Signed-off-by: Adam Wujek <adam.wujek@cern.ch>