storage/client should retry requests

[ptrus]

storage/client should be made to retry requests:

• for read - if none of requests succeed
• for write until F+1 requests succeed (related to: storage/client: Only wait for F+1 successful writes #1821)

Details:
Currently this can happen if connection to storage node is temporary non available:

{"caller":"balancer.go:130","level":"info","module":"grpc","msg":"base.baseBalancer: handle SubConn state change: 0xc0234a3990, TRANSIENT_FAILURE","ts":"2019-06-26T15:03:03.077707564Z"}
thread '<unnamed>' panicked at 'called `Result::unwrap()` on an `Err` value: ErrorMessage { msg: "rpc error: code = Unavailable desc = transport is closing" }

stack backtrace:
   0: failure::backtrace::internal::InternalBacktrace::new::h88fc859829218a81 (0x55e8566d7b19)
   1: failure::backtrace::Backtrace::new::hdbcb3dafa05cdaac (0x55e8566d7c19)', src/libcore/result.rs:999:5
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at ./cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.25/src/backtrace/libunwind.rs:97
   1: backtrace::backtrace::trace_unsynchronized
             at ./cargo/registry/src/github.com-1ecc6299db9ec823/backtrace-0.3.25/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:47
   3: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:36
   4: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:197
   5: std::panicking::default_hook