Update ps command in taskkill to also work on linux

tools/task_kill.py

 #!/usr/bin/env python
 #
 # Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 #
 
 # A script to kill hanging processs. The tool will return non-zero if any
 # process was actually found.
 #
@@ skipping 32 matching lines @@
                     help="Kill all dart processes")
   parser.add_option("--kill_browsers", default=False,
                      help="Kill all browser processes")
   (options, args) = parser.parse_args()
   return options
 
 
 def GetPidsPosix(process_name):
   # This is to have only one posix command, on linux we could just do:
   # pidof process_name
-  cmd = 'ps -e -o pid=,comm='
+  cmd = 'ps -e -o pid= -o comm='
   # Sample output:
   # 1 /sbin/launchd
   # 80943 /Applications/Safari.app/Contents/MacOS/Safari
   p = subprocess.Popen(cmd,
                        stdout=subprocess.PIPE,
                        stderr=subprocess.PIPE,
                        shell=True)
   output, stderr = p.communicate()
   results = []
   lines = output.splitlines()
@@ skipping 99 matching lines @@
   options = GetOptions()
   status = 0
   if (options.kill_dart):
     status += KillDart();
   if (options.kill_browsers):
     status += KillBrowsers()
   return status
 
 if __name__ == '__main__':
   sys.exit(Main())