[XENTOP] Adds batch mode processing option (output to stdout)

[XENTOP] Adds batch mode processing option (output to stdout)
to the xentop utility. It also adds the ability to specify the
number of iterations xentop should produce before exiting.

a) xentop -b

will output to stdout.

b) xentop -i <number>

will iterate <number> times and exit (option "n" is already used by
xentop. Hence the choice of "i"). This option can be used for both the
curses and batch modes.

From: Hariprasad Nellitheertha <mlisthari@gmail.com>
Signed-off-by: Keir Fraser <keir@xensource.com>