iperf: Fix data abort in iperf client.

iperf: Fix data abort in iperf client.

Following test cause data abort of iperf client.
iperf -s
iperf -c 127.0.0.1
iperf -c 127.0.0.1

Data abort can happen when iperf_run_client returns negative value.
In this case, iperf calls iperf_free_test -> iperf_client_end ->
iperf_free_test. This cause data abort because test is already freed
in iperf_free_test however iperf_client_end tries to use test pointer.
And also iperf_free_test tries to free again test pointer.
This patch re-organize the process this procedure.

Change-Id: I0ad6d986cd2457648eb2a99a078b8fa3af9e3ed7
Signed-off-by: EunBong Song <eunb.song@samsung.com>