MTL-1495 grep was reading "before" and not "after"

[rustydb]

Summary and Scope

• Fixes MTL-1495
• Relates to CAST-29116

Issue Type

• Bugfix Pull Request

This fixes grep to read from the desired segment, 2 lines after the
matching line. The problem here is grep is/was reading 2 lines before
the matching line, which reads from the wrong mdhandle. That misread
will fool the code to touching the wrong md handles.

Prerequisites

• I have included documentation in my PR (or it is not required)
• I tested this on internal system (x) (if yes, please include results or a description of the test)

Idempotency

Risks and Mitigations

This will mitigate waiting on RAIDs during reboots where the reboot was not necessarily clean.