xend: Receive error message of migration from destination server

xend: Receive error message of migration from destination server

The following error message was shown by xm migrate command.
In fact, I caused the command error by intention.  I prepared a
destination server where free memory was insufficient, and then
I tried to migrate a VM to the destination server.  As I had
expected, the command error occurred.  However the error message
was different from my expectation.  I would like to show an error
message from the destination server if an error occurred on the
destination server.

# xm migrate --live vm3 bx339
Error: (107, 'Transport endpoint is not connected')
Usage: xm migrate <Domain> <Host>

Migrate a domain to another machine.

Options:

-h, --help           Print this help.
-l, --live           Use live migration.
-p=3Dportnum, --port=3Dportnum
                     Use specified port for migration.
-n=3Dnodenum, --node=3Dnodenum
                     Use specified NUMA node on target.
-s, --ssl            Use ssl connection for migration.

If a destination server sends an error message, this patch shows=20
the error message.  For example, the following error message is=20
shown if free memory of the destination server is insufficient.

# xm migrate --live vm3 bx339
Error: I need 262144 KiB, but dom0_min_mem is 716800 and shrinking
to=20
716800 KiB would leave only 50368 KiB free. (from bx339)
Usage: xm migrate <Domain> <Host>

Migrate a domain to another machine.

Options:

-h, --help           Print this help.
-l, --live           Use live migration.
-p=3Dportnum, --port=3Dportnum
                     Use specified port for migration.
-n=3Dnodenum, --node=3Dnodenum
                     Use specified NUMA node on target.
-s, --ssl            Use ssl connection for migration.

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