test/perf: Disable periodic throughput reports to avoid vhost hang

It appears that if we run throughput tests with one-second periodic
reports, the sending side of the vhost channel used for SSH-based
command dispatch occasionally stops working altogether. I haven't
investigated this further, all I see is that output is truncated
at some point, and doesn't resume.

If we use gzip compression (ssh -C) this happens less frequently,
but it still happens, seemingly indicating the issue is probably
related to vhost itself.

Disable periodic reports in iperf3 clients. The -i options were
actually redundant, so remove them from both test files as well as
from test_iperf3().

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

test/lib/test

@@ -44,7 +44,7 @@ test_iperf3() {
 		 '('							\
 		 '	for i in $(seq 0 '${__procs}'); do'		\
 		 '		iperf3 -c '${__dest}' -p '${__port}	\
-		 '		  -t'${__time}' -T s${i} '"${@}"' &'	\
+		 '		 -t'${__time}' -i0 -T s${i} '"${@}"' &' \
 		 '	done;'						\
 		 '	wait'						\
 		 ')'