Fix Tokio issue with version > 0.1.11

[quentinlesceller]

Related to #2105 and #2128.
Currently with tokio semver >0.1.11 we experienced the following issue when refreshing the outputs:

20181208 23:09:08.734 ERROR grin_util::logger -
thread 'tokio-runtime-worker-1' panicked at 'nested block_on: EnterError { reason: "attempted to run an executor while another executor is already running" }': libcore/result.rs:1009stack backtrace:
   0:     0x5587172a5aed - backtrace::backtrace::trace::h33a8de1a5de4f598
   1:     0x5587172a4d02 - <backtrace::capture::Backtrace as core::default::Default>::default::h13bf884e561085be
   2:     0x5587172a4d79 - backtrace::capture::Backtrace::new::h810796244ae4b8f2
   3:     0x558717217450 - grin_util::logger::send_panic_to_log::{{closure}}::h4131e8199612a48b
   4:     0x558717373896 - std::panicking::rust_panic_with_hook::h71214e7ce0f7ac01
                        at libstd/panicking.rs:480
   5:     0x5587173733e1 - std::panicking::continue_panic_fmt::ha8b8442f4ea9bcac
                        at libstd/panicking.rs:390
   6:     0x5587173732c5 - rust_begin_unwind
                        at libstd/panicking.rs:325
   7:     0x5587173bcd6c - core::panicking::panic_fmt::h0c93626b89c38af6
                        at libcore/panicking.rs:77
   8:     0x558716ed1d96 - core::result::unwrap_failed::hd6d647e647f9d65f
   9:     0x558716ed38ea - tokio::runtime::Runtime::block_on::h50c07489d8a34431
  10:     0x558716e9ffbd - grin_api::client::send_request::h58cd94e37f2486a3
  11:     0x558716d17e1a - grin_api::client::get::hbbd2dcbfaea3a4b9
  12:     0x558716d1074b - <grin_wallet::node_clients::http::HTTPNodeClient as grin_wallet::libwallet::types::NodeClient>::get_chain_height::ha4a82fe83f2fb5e3
  13:     0x558716b1ce83 - grin_wallet::libwallet::internal::updater::refresh_outputs::he67ca7e885c2c77a
  14:     0x558716ac3eb2 - <grin_wallet::libwallet::api::APIOwner<W, C, K>>::retrieve_summary_info::h962086bf4a07c49c
  15:     0x558716b47742 - <grin_wallet::controller::OwnerAPIHandler<T, C, K> as grin_api::router::Handler>::get::h8becc02a4b5c4a18
  16:     0x558716b5d300 - grin_api::router::Handler::call::h3592fee7f16fbddf
  17:     0x558716e22e78 - <grin_api::router::Router as hyper::service::service::Service>::call::hbbd603eab9d00eef
  18:     0x558716ee6fd5 - <hyper::proto::h1::dispatch::Server<S> as hyper::proto::h1::dispatch::Dispatch>::recv_msg::hf8e1c05dc0b5c7f7
  19:     0x558716ef2400 - <hyper::proto::h1::dispatch::Dispatcher<D, Bs, I, T>>::poll_catch::h0e93e88a5683ce62
  20:     0x558716e8f6ae - <hyper::server::conn::upgrades::UpgradeableConnection<I, S, E> as futures::future::Future>::poll::h03c736ccad93c676
  21:     0x558716efc28a - <hyper::server::conn::spawn_all::NewSvcTask<I, N, S, E, W> as futures::future::Future>::poll::h7c7480fa1a02b78a
  22:     0x558717089761 - futures::task_impl::std::set::hc4b047e2258852d7
  23:     0x55871708a195 - <futures::task_impl::Spawn<T>>::poll_future_notify::h6b8b942bdee24293
  24:     0x55871708d9e0 - std::panicking::try::do_call::h379db939d220e7ba
  25:     0x558717385c99 - __rust_maybe_catch_panic
                        at libpanic_unwind/lib.rs:102
  26:     0x55871708b9fb - tokio_threadpool::task::Task::run::hd407da1872c403cb
  27:     0x558717083eb5 - tokio_threadpool::worker::Worker::run_task::h735b3514c6e90b44
  28:     0x55871708352e - tokio_threadpool::worker::Worker::run::ha56b3a90b49df5c9
  29:     0x558717069f45 - <std::thread::local::LocalKey<T>>::with::h2e2f8722784589ba
  30:     0x55871706a098 - <std::thread::local::LocalKey<T>>::with::h65ffeee491ed9b24
  31:     0x558717069d72 - <std::thread::local::LocalKey<T>>::with::h2207b72bbb3594a7
  32:     0x55871706cd5d - tokio::runtime::builder::Builder::build::{{closure}}::h33c8bf677f817e8b
  33:     0x55871708accc - <std::thread::local::LocalKey<T>>::with::h17a742e397d4af0c
  34:     0x55871708ae31 - <std::thread::local::LocalKey<T>>::with::h70802f72c7300a39
  35:     0x55871708e31b - std::sys_common::backtrace::__rust_begin_short_backtrace::he05acf4f68e09c1c
  36:     0x55871708d99b - std::panicking::try::do_call::h2a038064618082be
  37:     0x558717385c99 - __rust_maybe_catch_panic
                        at libpanic_unwind/lib.rs:102
  38:     0x55871708834f - <F as alloc::boxed::FnBox<A>>::call_box::h4ce92ff10f8c6050
  39:     0x55871736fe2d - <alloc::boxed::Box<(dyn alloc::boxed::FnBox<A, Output=R> + 'a)> as core::ops::function::FnOnce<A>>::call_once::he3acfc8f1203786f
                        at liballoc/boxed.rs:682
                         - std::sys_common::thread::start_thread::h5213f803a61d7811
                        at libstd/sys_common/thread.rs:24
  40:     0x55871735aeb5 - std::sys::unix::thread::Thread::new::thread_start::he89121f566d2a8c7
                        at libstd/sys/unix/thread.rs:90
  41:     0x7fdaab6636b9 - start_thread
  42:     0x7fdaab18341c - clone
  43:                0x0 - <unknown>

One possible solution would be to get rid of tokio/hyper altogether (#2040).

[quentinlesceller]

Closed for mimblewimble/grin-wallet#26.