vmd: fix rebooting a received vm

vmd: fix rebooting a received vm

Rebooting a received vm resulted in vmd(8) exiting as a result of
flawed state tracking in the parent process.

When stopping a vm, clear the VM_RECEIVE_STATE flag. When starting
a vm, make sure the parent process collapses any existing memory
ranges after the vm is sent to the vmm process (responsible for
launching the vm).

ok mlarkin@