Fix blink in watch command

The watch command uses a buffer instead of the standard output. Using this the watch
command can execute commands and wait the end of the execution to clear and print the buffer.
The watch command also catch cliException and KeyboardInterrupt in order to proceed to clean exit.

cccli/commands/watch.py

@@ -5,13 +5,14 @@
 CloudControl watch command
 '''
 
-import time as systime
+import sys
+import time
 
 from cccli.exception import *
 from sjrpc.core.exceptions import *
 from cccli.printer import Printer, color
 from cccli.command import OptionCommand
-
+from cStringIO import StringIO
 
 class Command_watch(OptionCommand):
     '''Show output of a repeated command'''
@@ -28,9 +29,23 @@ class Command_watch(OptionCommand):
         if len(self.args) == 0:
             raise cmdBadArgument()
         while True:
+            # Substitute aliases
             self.args = self.cli.aliases.substitute(self.args)
-            # Clear tty
-            self.cli.commands(["clear"])
-            # Execute command
-            self.cli.commands(self.args)
-            systime.sleep(self.options.seconds)
+            # Put the fd of a buffer in sys.stdout and sys.err instead of the tty fd
+            sys.stderr = sys.stdout = StringIO()
+            try:
+                # Clear tty
+                self.printer.clear()
+                # Execute command and write output in the buffer
+                self.cli.commands(self.args)
+                # Print the buffer
+                self.printer.out(sys.stdout.getvalue(), fd=sys.__stdout__)
+                # Wait
+                time.sleep(self.options.seconds)
+            except KeyboardInterrupt:
+                raise
+            except cliException:
+                raise
+            finally:
+                sys.stdout = sys.__stdout__
+                sys.stderr = sys.__stderr__