Automatic merge from submit-queue (batch tested with PRs 49861, 50933, 51380, 50688, 51305) refactor codes in volume iscsi to improve readability Signed-off-by: allencloud <allen.sun@daocloud.io> **What this PR does / why we need it**: This PR refactors some codes in pkg/volume/iscsi. What is specific, this PR takes advantage of return fast to make codes indent less. As a result the readability of codes will improve a little bit. What I did: 1. refactor codes in volume iscsi to improve readability. 2. change a keyword of `delete` into `deleteArgs` to reduce ambiguousness. 3. make some variables camel case. **Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes # NONE **Special notes for your reviewer**: NONE **Release note**: ```release-note NONE ```