test/crimson: fix a compiler error.

test/crimson: fix a compiler error.

When with -DWITH_SEASTAR=ON, met the following bug:
/home/ceph/src/test/crimson/test_alien_echo.cc:164:13: error: ‘client’ was not declared in this scope
             client.msgr->set_require_authorizer(false);
             ^~~~~~
/home/ceph/src/test/crimson/test_alien_echo.cc:164:13: note: suggested alternative: ‘client_t’
             client.msgr->set_require_authorizer(false);
             ^~~~~~
             client_t
/home/ceph/src/test/crimson/test_alien_echo.cc: In instantiation of ‘seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)>::<lambda(auto:48&)> [with auto:48 = seastar_pingpong::Client; auto:47 = ceph::net::Messenger*]’:
/usr/include/c++/7/type_traits:2428:26:   required by substitution of ‘template<class _Fn, class ... _Args> static std::__result_of_success<decltype (declval<_Fn>()((declval<_Args>)()...)), std::__invoke_other> std::__result_of_other_impl::_S_test(int) [with _Fn = seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)> [with auto:47 = ceph::net::Messenger*]::<lambda(auto:48&)>; _Args = {seastar_pingpong::Client&}]’
/usr/include/c++/7/type_traits:2439:55:   required from ‘struct std::__result_of_impl<false, false, seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)> [with auto:47 = ceph::net::Messenger*]::<lambda(auto:48&)>, seastar_pingpong::Client&>’
/usr/include/c++/7/type_traits:2444:12:   required from ‘struct std::__invoke_result<seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)> [with auto:47 = ceph::net::Messenger*]::<lambda(auto:48&)>, seastar_pingpong::Client&>’
/usr/include/c++/7/type_traits:2457:12:   required from ‘class std::result_of<seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)> [with auto:47 = ceph::net::Messenger*]::<lambda(auto:48&)>(seastar_pingpong::Client&)>’
/home//ceph/src/seastar/include/seastar/core/do_with.hh:93:17:   required from ‘auto seastar::do_with(T&&, F&&) [with T = seastar_pingpong::Client; F = seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)> [with auto:47 = ceph::net::Messenger*]::<lambda(auto:48&)>]’
/home/ceph/src/test/crimson/test_alien_echo.cc:184:32:   required from ‘seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)> [with auto:47 = ceph::net::Messenger*]’
/usr/include/c++/7/type_traits:2428:26:   required by substitution of ‘template<class _Fn, class ... _Args> static std::__result_of_success<decltype (declval<_Fn>()((declval<_Args>)()...)), std::__invoke_other> std::__result_of_other_impl::_S_test(int) [with _Fn = seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)>; _Args = {ceph::net::Messenger*&&}]’
/usr/include/c++/7/type_traits:2439:55:   required from ‘struct std::__result_of_impl<false, false, seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)>, ceph::net::Messenger*&&>’
/usr/include/c++/7/type_traits:2444:12:   required from ‘struct std::__invoke_result<seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)>, ceph::net::Messenger*&&>’
/usr/include/c++/7/type_traits:2457:12:   required from ‘class std::result_of<seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)>(ceph::net::Messenger*&&)>’
/home//ceph/src/seastar/include/seastar/core/future.hh:980:30:   required by substitution of ‘template<class Func, class Result>  requires  CanApply<Func, ceph::net::Messenger*> Result seastar::future<ceph::net::Messenger*>::then<Func, Result>(Func&&) [with Func = seastar_echo(entity_addr_t, echo_role, unsigned int)::<lambda(auto:47)>; Result = <missing>]’
/home//ceph/src/test/crimson/test_alien_echo.cc:207:8:   required from here
/home/ceph/src/test/crimson/test_alien_echo.cc:190:13: error: base operand of ‘->’ has non-pointer type ‘ceph::net::Messenger’
             client.msgr->set_require_authorizer(false);
             ^~~~~~

Signed-off-by: Jianpeng Ma <jianpeng.ma@intel.com>