fix #87 hostname shouldn't be written in server.IP field

[serdarkalayci]

Writing hostname to the IP field creates logs like the one below:

{"@timestamp":"2020-10-21T14:02:51.7698395+03:00","log.level":"Information","message":"Request starting HTTP/1.1 GET http://10.132.4.163:5111/readiness ","_metadata":{"message_template":"{HostingRequestStartingLog:l}","protocol":"HTTP/1.1","method":"GET","content_type":null,"content_length":null,"scheme":"http","path_base":"","path":"/readiness","query_string":"","hosting_request_starting_log":"Request starting HTTP/1.1 GET http://10.132.4.163:5111/readiness ","event_id":{"id":1},"request_id":"0HM3LHKKTLRML:00000001","request_path":"/readiness","span_id":"|3d1c3928-4b1f17b80024b28b.","trace_id":"3d1c3928-4b1f17b80024b28b","parent_id":"","connection_id":"0HM3LHKKTLRML"},"ecs":{"version":"1.5.0"},"event":{"severity":2,"timezone":"GMT+03:00","created":"2020-10-21T14:02:51.7698395+03:00"},"log":{"logger":"Microsoft.AspNetCore.Hosting.Diagnostics","original":null},"process":{"thread":{"id":25},"pid":1,"name":"dotnet","executable":"dotnet"},"server":{"address":"10.132.4.163:5111","ip":"10.132.4.163:5111"}}

which is not parsable as IP
"failed to parse field [server.ip] of type [ip] in document with id '3TwkS3UBbmzuC991IrD5'. Preview of field's value: '10.132.4.163:5111'","caused_by":{"type":"illegal_argument_exception","reason":"'10.132.4.163:5111' is not an IP string literal."}

[apmmachine]

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• Build Cause: [Branch indexing]

• Start Time: 2020-11-12T00:17:08.303+0000

• Duration: 10 min 15 sec

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Test	Results
Failed	0
Passed	70
Skipped	4
Total	74

[Mpdreamz]

LGTM, host can be an IP but we should treat this as incidental.

[Mpdreamz]

@serdarkalayci mind signing the https://www.elastic.co/contributor-agreement so that I may pull these bits in?

[Mpdreamz]

Thanks for signing @serdarkalayci (and the fix of course 😄)