VMState test: hmp interface for period update

Signed-off-by: Sanidhya Kashyap <sanidhya.iiith@gmail.com>
VMState test: cancel mechanism for an already running vmstate testing process

Signed-off-by: Sanidhya Kashyap <sanidhya.iiith@gmail.com>
VMState test: hmp interface for cancel mechanism

Signed-off-by: Sanidhya Kashyap <sanidhya.iiith@gmail.com>