Stringify database configurations

[gmcgibbon]

Allows configurations to be assigned as symbolized hashes as in

rails/actionview/test/active_record_unit.rb

Lines 48 to 52 in 0627442

	defaults = { database: ":memory:" }
	adapter = defined?(JRUBY_VERSION) ? "jdbcsqlite3" : "sqlite3"
	options = defaults.merge adapter: adapter, timeout: 500
	ActiveRecord::Base.establish_connection(options)
	ActiveRecord::Base.configurations = { "sqlite3_ar_integration" => options }

Without this, sometimes ActiveRecord::DatabaseConfigurations can think that a configuration is a URL config when its really a hash config.

r? @eileencodes
/cc @rafaelfranca

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