[WIP] Remove lio_iblock usage in lio-t implementation of iSCSILogicalUnit

[fpiecka]

lio_iblock parameter is used in iSCSILogicalUnit_start(), although it is unsupported in lio-t implementation (see iSCSILogicalUnit_validate()).

This PR removes the use of lio_iblock and instead tries to autodetect the backstore index (for lio-t only).

Indexes are assigned sequentially and their value depends on the order in which the backstores are created by targetcli (i.e. on the order in which resources are started).

In current implementation, only 1 LUN resource based on lio-t works (tested in CentOS 8). The second one fails to start as it has a higher index than 0.

I believe this PR should resolve #1256.

[knet-ci-bot]

Can one of the admins verify this patch?

[fpiecka]

This PR seems a bit unambitios when compared with #1072 which would solve the problem too. I'll ask the author whether ho could resolve the conflicts.