trace: fix level_span macros not propagating parents (#1167)

Currently, when the `trace_span!`, `debug_span!`, `info_span!`,
`warn_span!`, and `error_span!` macros are invoked with an explicit
parent, a name, and zero or more fields (no target), the macros don't
pass along the explicitly provided parent when expanding to the `span!`
macro. This is likely due to an oversight on my part.

This branch fixes these macros by adding the parent into the `span!`
macro expansion. I've also added a test to catch regressions

Shoutout to @jonhoo for catching this one!

Signed-off-by: Eliza Weisman <[email protected]>

tokio-trace/src/macros.rs

@@ -330,6 +330,7 @@ macro_rules! trace_span {
         span!(
             $crate::Level::TRACE,
             target: __tokio_trace_module_path!(),
+            parent: $parent,
             $name,
             $($field)*
         )
@@ -391,6 +392,7 @@ macro_rules! debug_span {
         span!(
             $crate::Level::INFO,
             target: __tokio_trace_module_path!(),
+            parent: $parent,
             $name,
             $($field)*
         )
@@ -452,6 +454,7 @@ macro_rules! info_span {
         span!(
             $crate::Level::INFO,
             target: __tokio_trace_module_path!(),
+            parent: $parent,
             $name,
             $($field)*
         )
@@ -513,6 +516,7 @@ macro_rules! warn_span {
         span!(
             $crate::Level::WARN,
             target: __tokio_trace_module_path!(),
+            parent: $parent,
             $name,
             $($field)*
         )
@@ -573,6 +577,7 @@ macro_rules! error_span {
         span!(
             $crate::Level::ERROR,
             target: __tokio_trace_module_path!(),
+            parent: $parent,
             $name,
             $($field)*
         )