Add timeout to iperf client starts

The WlanRebootTests and ChannelSweepTests were using the default timeout
of 3600 seconds for iperf. This meant any iperf issues would essentially
freeze the testbed. Updated both to use a 30 second timeout.

Bug: None
Test: Ran both the ChannelSweepTests and WlanRebootTests
Change-Id: I96a90ff55b0b11cc814ecb84103d3b08ebab49de
diff --git a/acts_tests/tests/google/fuchsia/wlan/performance/ChannelSweepTest.py b/acts_tests/tests/google/fuchsia/wlan/performance/ChannelSweepTest.py
index 91606d4..a674911 100644
--- a/acts_tests/tests/google/fuchsia/wlan/performance/ChannelSweepTest.py
+++ b/acts_tests/tests/google/fuchsia/wlan/performance/ChannelSweepTest.py
@@ -57,6 +57,7 @@
 
 DEFAULT_MIN_THROUGHPUT = 0
 DEFAULT_MAX_STD_DEV = 1
+DEFAULT_IPERF_TIMEOUT = 30
 
 DEFAULT_TIME_TO_WAIT_FOR_IP_ADDR = 30
 GRAPH_CIRCLE_SIZE = 10
@@ -334,13 +335,19 @@
                 'Running IPerf traffic from server (%s) to dut (%s).' %
                 (iperf_server_address, iperf_client_address))
             iperf_results_file = self.iperf_client.start(
-                iperf_server_address, '-i 1 -t 10 -R -J', 'channel_sweep_rx')
+                iperf_server_address,
+                '-i 1 -t 10 -R -J',
+                'channel_sweep_rx',
+                timeout=DEFAULT_IPERF_TIMEOUT)
         else:
             self.log.info(
                 'Running IPerf traffic from dut (%s) to server (%s).' %
                 (iperf_client_address, iperf_server_address))
             iperf_results_file = self.iperf_client.start(
-                iperf_server_address, '-i 1 -t 10 -J', 'channel_sweep_tx')
+                iperf_server_address,
+                '-i 1 -t 10 -J',
+                'channel_sweep_tx',
+                timeout=DEFAULT_IPERF_TIMEOUT)
         if iperf_results_file:
             iperf_results = IPerfResult(
                 iperf_results_file, reporting_speed_units=MEGABITS_PER_SECOND)
@@ -657,7 +664,8 @@
             base_message = (
                 'Actual throughput (on channel: %s, channel bandwidth: '
                 '%s, security: %s)' % (channel, channel_bandwidth, security))
-            if (tx_throughput < min_tx_throughput
+            if (not tx_throughput or not rx_throughput
+                    or tx_throughput < min_tx_throughput
                     or rx_throughput < min_rx_throughput):
                 asserts.fail('%s below the minimum threshold.' % base_message)
             asserts.explicit_pass('%s above the minimum threshold.' %