restore: get real pid for each task
util: remove unused the service fd constant
parasite: stop task on exit from a specified syscall

Currently a parasite stopped on sigreturn for unmaping a parasite blob.
parasite: add simplified version of parasite_prep_ctl

It will be used for unmaping restorer blob.
parasite: add a function for unmaping bootstrap blob
restore: save task state on pstree_item
restore: catch task on returning from sigreturn

A task is stopped here for unmaping restorer blob and restoring state.
restorer: unmap itself
parasite: unmap itself
debug
PTRACE_O_TRACESYSGOOD
cleanup