primary vm suspend/resume/checkpoint code

primary vm suspend/resume/checkpoint code

We will do the following things again and again:
1. Suspend primary vm
   a. Suspend primary vm
   b. do postsuspend
   c. Read CHECKPOINT_SVM_SUSPENDED sent by secondary
2. Checkpoint
   a. Write emulator xenstore data and emulator context
   b. Write checkpoint end record
3. Resume primary vm
   a. Read CHECKPOINT_SVM_READY from slave
   b. Do presume
   c. Resume primary vm
   d. Read CHECKPOINT_SVM_RESUMED from slave
4. Wait a new checkpoint
   a. Wait a new checkpoint(not implemented)
   b. Send CHECKPOINT_NEW to slave

Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
Signed-off-by: Yang Hongyang <hongyang.yang@easystack.cn>
Signed-off-by: Changlong Xie <xiecl.fnst@cn.fujitsu.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>