Add tag "slow" if span is considered slow

[quaff]

I'm using jaeger-ui, It can not query traces by span duration, but we could query traces by "slow=true" tag.

[coveralls]

Pull Request Test Coverage Report for Build 326

• 17 of 22 (77.27%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.2%) to 50.541%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/java/io/opentracing/contrib/jdbc/JdbcTracingUtils.java	17	22	77.27%
<!--	Total:	17	22	77.27%	-->

Totals
Change from base Build 324:	0.2%
Covered Lines:	514
Relevant Lines:	1017

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💛 - Coveralls

[pavolloffay]

@quaff jaeger can query spans by duration.

[quaff]

@quaff jaeger can query spans by duration.

Duration is whole trace duration not span duration.

[yurishkuro]

duration is for the selected service/operation, it applies anywhere in the trace

[quaff]

duration is for the selected service/operation, it applies anywhere in the trace

There are many operations including Query Update Execute Batch, I want query all slow operations in one query.

[quaff]

duration is for the selected service/operation, it applies anywhere in the trace

There are many operations including Query Update Execute Batch, I want query all slow operations in one query.

@yurishkuro Any thoughts?

[quaff]

@yurishkuro updated, thanks.