Stop using deprecated `path` field on Gitaly messages

What does this MR do?

Remove uses of deprecated path field on Gitaly messages. This revealed an error in our configuration generation in gitlab:gitaly:install rake task. The fix is included.

Are there points in the code the reviewer needs to double check?

No

Why was this MR needed?

We are changing to use storage names and relative paths to allow networked gitaly installations

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

gitaly#151 (closed)