conman:  Fix WLANConfiguration logging.

Change check_call to check_output so that on failure, the
CalledProcessError's output field will be set.

Change-Id: Iaaa0623502e015f103206440476fb81b84f8ad00
diff --git a/conman/connection_manager.py b/conman/connection_manager.py
index 93d1bef..488178c 100755
--- a/conman/connection_manager.py
+++ b/conman/connection_manager.py
@@ -97,7 +97,7 @@
     self.stop_client()
 
     try:
-      subprocess.check_call(self.command, stderr=subprocess.STDOUT)
+      subprocess.check_output(self.command, stderr=subprocess.STDOUT)
       self.access_point_up = True
       logging.debug('Started %s GHz AP', self.band)
     except subprocess.CalledProcessError as e:
@@ -112,7 +112,7 @@
       command += ['--interface_suffix', self.interface_suffix]
 
     try:
-      subprocess.check_call(command, stderr=subprocess.STDOUT)
+      subprocess.check_output(command, stderr=subprocess.STDOUT)
       self.access_point_up = False
       logging.debug('Stopped %s GHz AP', self.band)
     except subprocess.CalledProcessError as e:
@@ -132,7 +132,7 @@
     if self.passphrase:
       env['WIFI_CLIENT_PSK'] = self.passphrase
     try:
-      subprocess.check_call(command, stderr=subprocess.STDOUT, env=env)
+      subprocess.check_output(command, stderr=subprocess.STDOUT, env=env)
       self.client_up = True
       logging.info('Started wifi client on %s GHz', self.band)
     except subprocess.CalledProcessError as e:
@@ -146,7 +146,7 @@
     self.wifi.detach_wpa_control()
 
     try:
-      subprocess.check_call(self.WIFI_STOPCLIENT + ['-b', self.band],
+      subprocess.check_output(self.WIFI_STOPCLIENT + ['-b', self.band],
                             stderr=subprocess.STDOUT)
       self.client_up = False
       logging.debug('Stopped wifi client on %s GHz', self.band)