Fix some tests failure with GDB 8.0

Fix some tests failure with GDB 8.0

At the beginning of a Valgrind gdbserver test,
2 messages are produced when launching the command
   target remote | vgdb

A message output by vgdb:
   relaying data between gdb and process <pid>
(this message is read by GDB from the vgdb pipe, and re-output
on stderr)
and a message produced by GDB:
   Remote debugging using | ./vgdb

GDB 8.0 changes the order in which the above messages are output.
This causes 2 tests to fail, as the 'relaying' line appears
then in a part of the output deleted by a filter script.

To avoid this, change the filter scripts to always remove
this 'relaying line', which is not particularly interesting to check.
All the .exp files containining such a 'relaying' line are updated
accordingly.

This has been tested with various gdb versions (7.5, 7.7, 7.12, 8.0)
on amd64 and/or ppc64.

Thanks to Mark Wielaard, which helped to investigate this problem
by bisecting the GDB patches in GDB 8.0 causing this change of
behaviour.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@16453