services/horizon: Suppress stellar-core unreachable error when horizon is building state

[urvisavla]

PR Checklist

PR Structure

• This PR has reasonably narrow scope (if not, break it down into smaller PRs).
• This PR avoids mixing refactoring changes with feature changes (split into two PRs
  otherwise).
• This PR's title starts with name of package that is most changed in the PR, ex.
  services/friendbot, or all or doc if the changes are broad or impact many
  packages.

Thoroughness

• This PR adds tests for the most critical parts of the new functionality or fixes.
• I've updated any docs (developer docs, .md
  files, etc... affected by this change). Take a look in the docs folder for a given service,
  like this one.

Release planning

• I've updated the relevant CHANGELOG (here for Horizon) if
  needed with deprecations, added features, breaking changes, and DB schema changes.
• I've decided if this PR requires a new major/minor version according to
  semver, or if it's mainly a patch change. The PR is targeted at the next
  release branch if it's not a patch change.

What

Added checks for to avoid logging "could not load stellar-core info" errors when Horizon is in the build state

Why

When we fixed issue #4446, we missed another place where we are attempting to get core info and the same condition is applied i.e. if core is blocked, we log an error. This error is confusing for users (from discord) because it leads them to think that they needed to explicitly run core process, but that is not the case.

Known limitations

As in #4860, we skip querying core so even if core is reachable, we will not update core info. Alternative would be to only perform the checks if there is an error and decide whether to suppress the error or not.