CA-210336: Added exception handling to prevent stack trace dump

Added a try-except block around line 353 which lists devices
at a given path in BaseISCSI.py attach method.

Signed-off-by: Letsibogo Ramadi <letsibogo.ramadi@citrix.com>

Author: letsboogey

drivers/BaseISCSI.py

@@ -350,7 +350,14 @@ def attach(self, sr_uuid):
         if self.dconf.has_key('SCSIid'):
             if self.mpath == 'true':
                 self.mpathmodule.refresh(self.dconf['SCSIid'], 0)
-            devs = os.listdir("/dev/disk/by-scsid/%s" % self.dconf['SCSIid'])
+            try:
+                devs_path = "/dev/disk/by-scsid/%s" % self.dconf['SCSIid']
+                devs = os.listdir(devs_path)
+            except:
+                util.SMlog("[Errno 2] No such file or directory: '%s'" % devs_path)
+                raise xs_errors.XenError('ConfigDeviceInvalid',
+                                                 opterr='check devices path')
+
             for dev in devs:
                 realdev = os.path.realpath("/dev/disk/by-scsid/%s/%s" % (self.dconf['SCSIid'], dev))
                 util.set_scheduler(realdev.split("/")[-1], "noop")