veyron/runtimes/google/rt: make default top-level vtrace span be called <empty string>
We're including the names vtrace spans in errors automatically.
The top-level vtrace span was called "Root", which was thus showing up
in error messages when no other span had been created. This change
alters the name of the top-level span to be <empty string>
(in veyron/runtimes/google/rt/ipc.go).
The changes in veyron/runtimes/google/ipc/context_test.go and
veyron/runtimes/google/vtrace/vtrace_test.go are optional. They just change
the tests so that they use the same convention as the normal setting.
Change-Id: I31c3b5b6f62c139eeeb0501ec5215d088610fd86
3 files changed
