Add a space
Added a exists API to tracer so that clients can check if a
trace is running/getting ready to run without having to do
the whole fetch trace drama
Changed worker code to check if a live trace exists rather
than using run which checks for the sampling co-efficient
which will likely return false. Checking if a live trace
exists is the most accurate option
Pid, hostname are now part of a metadata class. In this
way they can be used where needed and don't have to be
computed every time we check Tracer.run? or create a
new span