[feature] allow to overwrite primary_conninfo in restored instance

[gsmolk]

Useful for restoring cluster members.
branch: https://github.com/postgrespro/pg_probackup/tree/issue_171

[gsmolk]

I think, we should be checking that primary_conninfo, provided by user, is valid.

[gsmolk]

Merged.