[box] add tests for config reloading

test/box/recfg.result

+reload configuration
+fail
+	Could not accept read only 'slab_alloc_arena' option
+	Could not accept read only 'pid_file' option
+	Could not accept read only 'primary_port' option
+	Could not accept read only 'secondary_port' option
+	Could not accept read only 'admin_port' option
+	Could not accept read only 'rows_per_wal' option
+	Could not accept read only 'namespace[0].enabled' option
+	Could not accept read only 'namespace[0].index[0].type' option
+	Could not accept read only 'namespace[0].index[0].unique' option
+	Could not accept read only 'namespace[0].index[0].key_field[0].fieldno' option
+	Could not accept read only 'namespace[0].index[0].key_field[0].type' option
+---
+reload configuration
+fail
+	Option 'namespace[0].enabled' is not set (or has a default value)
+---
+reload configuration
+ok

test/box/recfg.test

+# encoding: tarantool
+#
+os.rename("var/tarantool.cfg", "var/tarantool.cfg.old")
+
+os.symlink("../box/tarantool_bad1.cfg", "var/tarantool.cfg")
+exec admin "reload configuration"
+
+os.unlink("var/tarantool.cfg")
+os.symlink("../box/tarantool_bad2.cfg", "var/tarantool.cfg")
+exec admin "reload configuration"
+
+os.unlink("var/tarantool.cfg")
+os.symlink("../box/tarantool_good.cfg", "var/tarantool.cfg")
+exec admin "reload configuration"
+
+os.unlink("var/tarantool.cfg")
+os.rename("var/tarantool.cfg.old", "var/tarantool.cfg")
+# vim: syntax=python

test/box/tarantool_bad1.cfg

+slab_alloc_arena = 0.2
+
+pid_file = "/var/run/box.pid"
+
+primary_port = 33023
+secondary_port = 33024
+admin_port = 33025
+
+rows_per_wal = 500
+
+namespace[0].enabled = 0
+namespace[0].index[0].type = "TREE"
+namespace[0].index[0].unique = 0
+namespace[0].index[0].key_field[0].fieldno = 1
+namespace[0].index[0].key_field[0].type = "STR"
+

test/box/tarantool_bad2.cfg

+slab_alloc_arena = 0.1
+
+pid_file = "box.pid"
+
+primary_port = 33013
+secondary_port = 33014
+admin_port = 33015
+
+rows_per_wal = 50
+
+#namespace[0].enabled = 1
+namespace[0].index[0].type = "HASH"
+namespace[0].index[0].unique = 1
+namespace[0].index[0].key_field[0].fieldno = 0
+namespace[0].index[0].key_field[0].type = "NUM"
+

test/box/tarantool_good.cfg

+slab_alloc_arena = 0.1
+
+pid_file = "box.pid"
+
+primary_port = 33013
+secondary_port = 33014
+admin_port = 33015
+
+rows_per_wal = 50
+
+namespace[0].enabled = 1
+namespace[0].index[0].type = "HASH"
+namespace[0].index[0].unique = 1
+namespace[0].index[0].key_field[0].fieldno = 0
+namespace[0].index[0].key_field[0].type = "NUM"
+