Cartridge role incompatible with http_enabled = false

[rosik]

Given the following init.lua:

cartridge.cfg({
    roles = {
        'cartridge.roles.metrics',
    },
})

Cartridge fails to start with http_enabled = false:

2021-04-07 17:55:47.891 [12319] main utils.c:1014 E> LuajitError: ...myapp/.rocks/share/tarantool/cartridge/roles/metrics.lua:93: attempt to index local 'httpd' (a nil value)
2021-04-07 17:55:47.891 [12319] main F> fatal error, exiting the event loop

This case should be valid