Add logutil.LogByLine to avoid log truncation on logging SetRequests.

[wenovus]

Some systems have a limit. This is currently hardcoded to 15000 bytes.

I0131 14:47:31.909694 2538970 logutil.go:27] SetRequest:
I0131 14:47:31.909705 2538970 logutil.go:27] prefix:  {
I0131 14:47:31.909712 2538970 logutil.go:27]   target:  "dut"
I0131 14:47:31.909719 2538970 logutil.go:27] }
I0131 14:47:31.909726 2538970 logutil.go:27] delete:  {
I0131 14:47:31.909734 2538970 logutil.go:27]   origin:  "openconfig"
I0131 14:47:31.909741 2538970 logutil.go:27]   elem:  {
I0131 14:47:31.909748 2538970 logutil.go:27]     name:  "parent"
I0131 14:47:31.909755 2538970 logutil.go:27]   }
I0131 14:47:31.909763 2538970 logutil.go:27]   elem:  {
I0131 14:47:31.909770 2538970 logutil.go:27]     name:  "child"
I0131 14:47:31.909777 2538970 logutil.go:27]   }
I0131 14:47:31.909784 2538970 logutil.go:27]   elem:  {
I0131 14:47:31.909791 2538970 logutil.go:27]     name:  "config"
I0131 14:47:31.909799 2538970 logutil.go:27]   }
I0131 14:47:31.909806 2538970 logutil.go:27]   elem:  {
I0131 14:47:31.909813 2538970 logutil.go:27]     name:  "one"
I0131 14:47:31.909820 2538970 logutil.go:27]   }
I0131 14:47:31.909828 2538970 logutil.go:27] }
I0131 14:47:31.909835 2538970 logutil.go:27] update:  {
I0131 14:47:31.909842 2538970 logutil.go:27]   path:  {
I0131 14:47:31.909849 2538970 logutil.go:27]     origin:  "openconfig"
I0131 14:47:31.909856 2538970 logutil.go:27]     elem:  {
I0131 14:47:31.909876 2538970 logutil.go:27]       name:  "parent"
I0131 14:47:31.909881 2538970 logutil.go:27]     }
I0131 14:47:31.909886 2538970 logutil.go:27]     elem:  {
I0131 14:47:31.909891 2538970 logutil.go:27]       name:  "child"
I0131 14:47:31.909897 2538970 logutil.go:27]     }
I0131 14:47:31.909902 2538970 logutil.go:27]   }
I0131 14:47:31.909907 2538970 logutil.go:27]   val:  {
I0131 14:47:31.909912 2538970 logutil.go:27]     json_ietf_val:  "{\n  \"openconfig-simple:config\": {\n    \"one\": \"foo\"\n  }\n}"
I0131 14:47:31.909917 2538970 logutil.go:27]   }
I0131 14:47:31.909922 2538970 logutil.go:27] }
I0131 14:47:31.909927 2538970 logutil.go:27] -------delete path #0------
I0131 14:47:31.909932 2538970 logutil.go:27] /parent/child/config/one
I0131 14:47:31.909937 2538970 logutil.go:27] -------update path/value pair #0------
I0131 14:47:31.909943 2538970 logutil.go:27] /parent/child
I0131 14:47:31.909948 2538970 logutil.go:27] {
I0131 14:47:31.909953 2538970 logutil.go:27]   "openconfig-simple:config": {
I0131 14:47:31.909958 2538970 logutil.go:27]     "one": "foo"
I0131 14:47:31.909963 2538970 logutil.go:27]   }
I0131 14:47:31.909968 2538970 logutil.go:27] }

[coveralls]

Pull Request Test Coverage Report for Build 4059050107

• 2 of 2 (100.0%) changed or added relevant lines in 2 files are covered.
• 10 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 83.992%

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Files with Coverage Reduction	New Missed Lines	%
ygnmi/gnmi.go	10	88.82%

Totals
Change from base Build 4057419380:	0.02%
Covered Lines:	1679
Relevant Lines:	1999

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💛 - Coveralls