add GlobalTracer support

[malafeev]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 41

• 0 of 111 (0.0%) changed or added relevant lines in 3 files are covered.
• 5 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 1.087%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
opentracing-redis-lettuce/src/main/java/io/opentracing/contrib/redis/lettuce/TracingStatefulRedisConnection.java	0	2	0.0%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisSentinelPool.java	0	26	0.0%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisPool.java	0	83	0.0%

Files with Coverage Reduction	New Missed Lines	%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisSentinelPool.java	1	18.81%
opentracing-redis-jedis/src/main/java/io/opentracing/contrib/redis/jedis/TracingJedisPool.java	4	8.2%

Totals
Change from base Build 39:	-0.01%
Covered Lines:	114
Relevant Lines:	10487

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💛 - Coveralls