converted "command" to "shell" so that "sleep ; ,," will work

roles/mellanox_drivers/tasks/main.yml

 ---
 - include_vars: mellanoxVars.yml
 
-
 - name: yum install dependencies
   yum:  name=perl,pciutils,gtk2,atk,cairo,gcc-gfortran,libxml2-python,tcsh,libnl,lsof,tcl,tk
   sudo: true
@@ -105,9 +104,9 @@
 # A REBOOT IS NEEDED AFTER SUCCESSFUL INSTALL
 #
 - name: restart machine
-  command: "sleep 5; sudo shutdown -r now"
+  shell: "sleep 5; sudo shutdown -r now"
   async: 2
-  poll: 0
+  poll: 1
   ignore_errors: true
   sudo: true
   when: ansible_os_family=="RedHat" and  drivers_installed|failed