vzctl: save a pid of init in a state file

CRIU requires a pid of the init.
vzctl: split ct_env_create

ct_env_create will able to execute CT and to resume CT
vzctl: save PID of init in a state file

It will be used for checkpointing this CT
vzctl: split vps_chkpnt and vps_restore

It's a preparation for moving vz-specific code in hook_vz.c.
vzctl: move cpt/rst code in hook_vz
vzctl: transfer fs in vps_chkpnt, vps_restore, env_start_FN
vzctl: checkpoint/restoer of upstream CTs

It can be done by any third party tools.
sripts/ct-cpt and script/ct_rst are executed to dump and restore CT
This patch adds scripts for CRIU.

v2: add the GPL header and descriptions in scripts
    describe and check variables in scripts