Validate jib during jail import

[JRGTH]

This import enhancement will locate/install the jib script required by VNET jails.

Issue/Bug reference: #597

[joh-ku]

Hi @JRGTH, thanks for the quick PR. For the avoidance of redundant code, wouldn't it be sufficient to check for jib in start.sh only?

[JRGTH]

Hi @joh-ku, The jib command should be installed just once upon a VNET jail creation or a VNET jail import(bug fix issued) as you've reported, unless manually installed by user.

Also yes the jib validation can be done in the start.sh command as well but if the user have lots of VNET jails this may lead for several grep command executions which is unnecessary.

[joh-ku]

Understood, thank you for the clarification.