Use relative path to sqlite3 db in `rails db` command

Rails uses sqlit3 db file with a path relative to the rails root. It
allows to execute server not from rails root only. For example you
can fire `./spec/dummy/script/rails s` to start dummy application
server if you develop some engine gem.

Now the `rails db` command uses relative paths also and you can explore
your dummy db via `./spec/dummy/script/rails db` command.

railties/lib/rails/commands/dbconsole.rb

@@ -96,7 +96,7 @@ def start
 
         args << "-#{options['mode']}" if options['mode']
         args << "-header" if options['header']
-        args << config['database']
+        args << File.expand_path(config['database'], Rails.root)
 
         find_cmd_and_exec('sqlite3', *args)
 

railties/test/commands/dbconsole_test.rb

@@ -92,20 +92,25 @@ def test_sqlite
   end
 
   def test_sqlite3
-    dbconsole.expects(:find_cmd_and_exec).with('sqlite3', 'db')
-    start(adapter: 'sqlite3', database: 'db')
+    dbconsole.expects(:find_cmd_and_exec).with('sqlite3', Rails.root.join('db.sqlite3').to_s)
+    start(adapter: 'sqlite3', database: 'db.sqlite3')
     assert !aborted
   end
 
   def test_sqlite3_mode
-    dbconsole.expects(:find_cmd_and_exec).with('sqlite3', '-html', 'db')
-    start({adapter: 'sqlite3', database: 'db'}, ['--mode', 'html'])
+    dbconsole.expects(:find_cmd_and_exec).with('sqlite3', '-html', Rails.root.join('db.sqlite3').to_s)
+    start({adapter: 'sqlite3', database: 'db.sqlite3'}, ['--mode', 'html'])
     assert !aborted
   end
 
   def test_sqlite3_header
-    dbconsole.expects(:find_cmd_and_exec).with('sqlite3', '-header', 'db')
-    start({adapter: 'sqlite3', database: 'db'}, ['--header'])
+    dbconsole.expects(:find_cmd_and_exec).with('sqlite3', '-header', Rails.root.join('db.sqlite3').to_s)
+    start({adapter: 'sqlite3', database: 'db.sqlite3'}, ['--header'])
+  end
+
+  def test_sqlite3_db_absolute_path
+    dbconsole.expects(:find_cmd_and_exec).with('sqlite3', '/tmp/db.sqlite3')
+    start(adapter: 'sqlite3', database: '/tmp/db.sqlite3')
     assert !aborted
   end