put Snapshot feature option afer File Support

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>
revert process-list

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>
initialize function pointers to NULL if feature disabled

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>
comments to driver interfaces of the shared memory snapshot feature 

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>
fix comparison operation conventions

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>
fix checking the return value of QMP snapshot-create

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>
fix indentation and extra lines

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>
fix endif wraps

Signed-off-by: Guanglin Xu <mzguanglin@gmail.com>