Honor --sql-host, --sql-port and --sql-db for SQL backup/restore (external PostgreSQL)

[edmharlaoag]

Problem

knife ec backup --with-user-sql does not honor the SQL connection flags
and silently targets the wrong PostgreSQL server and database:

• On external-PostgreSQL deployments it always connects to localhost:5432
  and fails with PG::ConnectionBad: Connection refused.
• The configured database name is ignored, so it connects to a database
  named after the SQL user — servers whose DB name differs from the user
  name can't be backed up at all (issue --sql-db does not take effect #181).

Root cause

Both problems live in EcKeyBase:

1. Host/port — load_config_from_file! autoconfigures sql_user/
   sql_password/sql_db from /etc/opscode/chef-server-running.json but
   never reads the PostgreSQL host or port, while --sql-host/
   --sql-port are declared with hardcoded localhost/5432 defaults that
   always populate the config — so the target can never be derived from the
   running config.

   Note: this is not a = vs ||= issue. sql_db already used ||=,
   and host/port were never assigned in the autoconfigure block; a ||=
   there would have been a no-op against the defaulted option.

2. Database name — #db builds the connection URI from host, port, user,
   password and query params, but never writes config[:sql_db] into the URI
   path, so the resolved database name is dropped and PostgreSQL falls back to
   a user-named database (--sql-db does not take effect #181).

Fix

• Remove the masking :default => "localhost"/5432 from the --sql-host/
  --sql-port options (ec_base.rb, ec_key_base.rb).
• Source sql_host/sql_port from private_chef.postgresql.vip/port in
  load_config_from_file!, using ||= so an explicit --sql-host/
  --sql-port still wins.
• Write the database name into the connection URI path in #db
  (server_uri.path = "/#{config[:sql_db]}" if config[:sql_db]) — the one-line
  fix originally proposed by @ioSpark in Pass --sql-db to URI builder if given #182.
• Fall back to localhost:5432 in #db when host/port are unset, preserving
  embedded-PostgreSQL behavior.

Backward compatibility

Embedded-PostgreSQL installs report a loopback vip, and the #db fallback
covers the Automate / no-running-config paths, so those deployments are
unaffected. Explicit CLI flags retain top precedence.

Tests

Adds specs for: host/port adoption from chef-server-running.json, explicit
--sql-host/--sql-port precedence, and the database name appearing in the
connection URI.

Fixes #181. Refs #182, chef/chef-server#2907.