[Sheepdog] [PATCH 0/5] support snapshot tag string

[FUJITA Tomonori]

This makes sheepdog snapshot logic more similar to qcow2. The two
major changes are: a snapshot tag is a string and a snapshot id is
automatically assigned.

fujita at rose:~/git/qemu-kvm$ qemu-img snapshot -c test3 sheepdog:linux

fujita at rose:~/git/qemu-kvm$ qemu-img snapshot -l sheepdog:linux
Snapshot list:
ID        TAG                 VM SIZE                DATE       VMCLOCK
1         test1                     0 2010-01-19 00:09:39   00:00:00.000
2         test2                     0 2010-01-19 00:10:34   00:00:00.000
3         test3                     0 2010-01-19 00:10:43   00:00:00.000

This mutually depends the patchset for sheepdog that I'll send soon.