lib.sh: make sure that the output.log directory exists
    
    Note that this is needed for the library unit test to work.
    The libraries are in upstream located in /usr/share/beakerlib-libraries
    instead of /mnt/tests folder.
    
    Also log information about the output.log path to user.
    
    Signed-off-by: Miroslav Vadkerti <mvadkert@redhat.com>