xentop: Dynamically expand some columns

xentop: Dynamically expand some columns

Allow certain xentop columns to automatically expand as the amount
of data reported gets larger.  The columns allowed to auto expand are:

NETTX(k), NETRX(k), VBD_RD, VBD_WR, VBD_RSECT, VBD_WSECT

If the -f option is used to allow full length VM names, those names will
also be aligned based on the longest name in the NAME column.

The default minimum width of all columns remains unchanged.

Signed-off-by: Markus Hauschild <Markus.Hauschild@rz.uni-regensburg.de>
Signed-off-by: Charles Arnold <carnold@suse.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>