xend: Fix for op_pincpu in SrvDomain.py

xend: Fix for op_pincpu in SrvDomain.py

op_pincpu method in SrvDomain.py does not currently work because
op_pincpu method gives string objects to a cpumap argument of
domain_pincpu method in XendDomain.py though the cpumap argument
expects list objects.

This patch solves the above problem as follows.

op_pincpu method gives string objects to the cpumap argument as is,
because op_pincpu method cannot give list objects to the cpumap
argument.
Instead, domain_pincpu method expects that the cpumap argument is
string objects, then domain_pincpu method converts the cpumap
argument into list objects.
Also, the patch modifies two methods (except for op_pincpu method)
calling domain_pincpu method.  The methods give string objects to
the cpumap argument instead of list objects.

Signed-off-by: Masaki Kanno <kanno.masaki@jp.fujitsu.com>