upgrade to 1.5.1 and do some refactors

[luyiisme]

Motivation:

optimze

Modification:

• Reduce configuration operations when use DefaultLookoutclient and lookoutRegistry;
• Fix a debug log NPE （in 1.5.0） ，when check a valid gateway server；
• Upgrade client version to 1.5.1

[coveralls]

Pull Request Test Coverage Report for Build 93

• 16 of 19 (84.21%) changed or added relevant lines in 5 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.06%) to 67.795%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
client/lookout-reg-server/src/main/java/com/alipay/lookout/remote/report/support/http/ReportDecider.java	7	8	87.5%
client/lookout-reg-server/src/main/java/com/alipay/lookout/remote/report/support/http/DefaultHttpRequestProcessor.java	5	7	71.43%

Files with Coverage Reduction	New Missed Lines	%
client/lookout-reg-server/src/main/java/com/alipay/lookout/remote/report/support/http/DefaultHttpRequestProcessor.java	2	51.58%

Totals
Change from base Build 91:	0.06%
Covered Lines:	2583
Relevant Lines:	3810

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💛 - Coveralls