eCTS: Close tty

This patch makes cts.py close tty files explicitly.

BUG=none
BRANCH=none
TEST=cts.py -m meta

Change-Id: Ifebfdd9607a603075492a59b5fb588e3cbc4ab12
Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/544106
Reviewed-by: Randall Spangler <rspangler@chromium.org>

cts/common/board.py

@@ -81,8 +81,7 @@ class Board(object):
       List of serials
     """
     usb_args = ['lsusb', '-v', '-d', '0x0483:0x374b']
-    usb_process = sp.Popen(usb_args, stdout=sp.PIPE, shell=False)
-    st_link_info = usb_process.communicate()[0]
+    st_link_info = sp.check_output(usb_args)
     st_serials = []
     for line in st_link_info.split('\n'):
       if 'iSerial' not in line:
@@ -254,6 +253,10 @@ class Board(object):
     fcntl.fcntl(fd, fcntl.F_SETFL, flag | os.O_NONBLOCK)
     return fd
 
+  def close_tty(self):
+    """Close tty"""
+    os.close(self.tty)
+
 
 class TestHarness(Board):
   """Subclass of Board representing a Test Harness.

cts/cts.py

@@ -335,8 +335,10 @@ class Cts(object):
 
     print 'Reading DUT tty...'
     dut_output, _ = self.dut.read_tty()
+    self.dut.close_tty()
     print 'Reading TH tty...'
     th_output, _ = self.th.read_tty()
+    self.th.close_tty()
 
     print 'Halting TH...'
     if not self.th.send_open_ocd_commands(['init', 'reset halt']):