tests: ipc: avoid problems when UNIX_PATH_MAX (108) limits is hit
tests: ipc: avoid problems when UNIX_PATH_MAX (108) limits is hit

There's some slight reserve for when bigger PID ranges are in use.
The method to yield the limit on prefix string was derived from
practical experience (rather than based on exact calculations).

Signed-off-by: Jan Pokorný <f06ec55ecfb6704a26166905f43ade3ead1f75d3@redhat.com>

kgaillot/libqb,ClusterLabs/libqb,ClusterLabs/libqb,kgaillot/libqb,kgaillot/libqb,ClusterLabs/libqb