Ignore blocked trace stack by default

[prashantv]

When running tests with -trace, a background
goroutine blocks on runtime.ReadTrace:

Goroutine 20 in state trace reader (blocked), with runtime.goparkunlock on top of the stack:
goroutine 20 [trace reader (blocked)]:
runtime.goparkunlock(...)
	(truncated)/go1.13.linux.amd64/src/runtime/proc.go:310
runtime.ReadTrace(0xc00008e048, 0xc0000160d0, 0x10)
	(truncated)/go1.13.linux.amd64/src/runtime/trace.go:395 +0x4ed
runtime/trace.Start.func1(0x7b3dc0, 0xc00008e048)
	(truncated)/go1.13.linux.amd64/src/runtime/trace/trace.go:129 +0x47
created by runtime/trace.Start
	(truncated)/go1.13.linux.amd64/src/runtime/trace/trace.go:127 +0xd8

Skip this stack by default. Run tests with -trace enabled to verify
that this stack should be skipped.

Fixes #39.

[codecov]

Codecov Report

Merging #40 into master will increase coverage by 0.17%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master     #40      +/-   ##
=========================================
+ Coverage   95.03%   95.2%   +0.17%     
=========================================
  Files           4       4              
  Lines         141     146       +5     
=========================================
+ Hits          134     139       +5     
  Misses          4       4              
  Partials        3       3

Impacted Files	Coverage Δ
options.go	100% <100%> (ø)	⬆️

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[prashantv]

Capturing an offline discussion with @abhinav:

This is non-ideal, since it's just a string match against the entire stack, which is more likely to have false positives. As a follow up, filed #41 to parse the stack for better matching, but want to release this fix soon.