split config.in.spaces and partial index branches

cfg/tarantool_box_cfg.c

cfg/tarantool_box_cfg.h

doc/user/errcode.xml

doc/user/space.xml

include/errcode.h

mod/box/box_cfg.cfg_tmpl

mod/box/box_lua.h

mod/box/box_lua.m

mod/box/index.h

mod/box/index.m

mod/box/space.m

mod/box/tree.m

test/box/admin.result

test/box/configuration.result

test/box_big/part_index.test

test/box_big/tarantool.cfg

test/box_memcached/off.result