tools/xend, xm: add a command to get the state of VMs

tools/xend, xm: add a command to get the state of VMs

add a command "domstate" to get the state of Vms, which may have one state of
{'shutoff', 'idle','shutdown','running','crashed','paused' or 'paused by
admin"}.

For case of pause, I distinguish it into two conditions. One is "paused" the
other is "paused by admin".
"pasued by admin" means that users pause a domain voluntary by "xm paused
VM" or " API"

Signed-off-by James (Song Wei) <jsong@novell.com>