Fix gdb.multi/multi-term-settings.exp blocking under high load/slow gdb

Fix gdb.multi/multi-term-settings.exp blocking under high load/slow gdb

Similarly to multi-arch-exec.exp, increase the alarm timer to avoid
test blocking under high load or with a slow gdb.

2019-03-28  Philippe Waroquiers  <philippe.waroquiers@skynet.be>

	* gdb.multi/multi-term-settings.c (main): Increase alarm timer.