Remove --loglevel CLI flag

[wata727]

See also #1070

TFLint launches plugins as separate processes, so when setting log levels, an easy way to share between processes is to set an environment variable. As a matter of fact, currently, the log output is different depending on the setting with --loglevel and the setting with the TFLINT_LOG environment variable:

TFLINT_LOG

% cd integrationtest/inspection/basic
% TFLINT_LOG=trace tflint
15:18:12 config.go:115: [INFO] Load config: .tflint.hcl
15:18:12 config.go:242: [DEBUG] Config loaded
15:18:12 config.go:243: [DEBUG]   Module: false
15:18:12 config.go:244: [DEBUG]   Force: false
15:18:12 config.go:245: [DEBUG]   IgnoreModules:
15:18:12 config.go:249: [DEBUG]   Varfiles:
15:18:12 config.go:250: [DEBUG]   Variables:

...<snip>...

15:18:12 provider.go:92: [INFO]   5 default rules enabled
15:18:12 terraform_deprecated_interpolation.go:48: [TRACE] Check `terraform_deprecated_interpolation` rule for `root` runne
r
15:18:12 terraform_empty_list_equality.go:46: [TRACE] Check `terraform_empty_list_equality` rule for `root` runner
15:18:12 terraform_module_pinned_source.go:61: [TRACE] Check `terraform_module_pinned_source` rule for `root` runner
15:18:12 terraform_module_version.go:58: [TRACE] Check `terraform_module_version` rule for `root` runner
15:18:12 terraform_workspace_remote.go:50: [TRACE] Check `terraform_workspace_remote` rule for `root` runner
15:18:12 [DEBUG] host2plugin/client.go:101: starting host-side gRPC server
15:18:12 [DEBUG] runtime/asm_amd64.s:1571: tflint-ruleset-testing: 15:18:12 [TRACE] interceptor/logging.go:15: gRPC request
: direction=host2plugin method=/proto.RuleSet/Check req=runner:1
15:18:12 [TRACE] interceptor/logging.go:15: gRPC request: direction=plugin2host method=/proto.Runner/GetModuleContent req="
schema:{blocks:{type:\"resource\"  label_names:\"type\"  label_names:\"name\"  body:{attributes:{name:\"tags\"}}}}  option:
{module_ctx:MODULE_CTX_TYPE_SELF  hint:{resource_type:\"aws_autoscaling_group\"}}"
15:18:12 [TRACE] interceptor/logging.go:15: gRPC request: direction=plugin2host method=/proto.Runner/GetModuleContent req="
schema:{blocks:{type:\"resource\"  label_names:\"type\"  label_names:\"name\"  body:{attributes:{name:\"name\"}}}}  option:
{module_ctx:MODULE_CTX_TYPE_SELF  hint:{resource_type:\"aws_iam_policy\"}  include_not_created:true}"
15:18:12 [TRACE] interceptor/logging.go:15: gRPC request: direction=plugin2host method=/proto.Runner/GetModuleContent req="
schema:{blocks:{type:\"resource\"  label_names:\"type\"  label_names:\"name\"  body:{attributes:{name:\"instance_type\"}}}}
  option:{module_ctx:MODULE_CTX_TYPE_SELF  hint:{resource_type:\"aws_instance\"}}"
15:18:12 [TRACE] interceptor/logging.go:15: gRPC request: direction=plugin2host method=/proto.Runner/GetFile req="name:\"te
mplate.tf\""

...<snip>...

15:18:12 [TRACE] interceptor/logging.go:15: gRPC request: direction=plugin2host method=/proto.Runner/GetModuleContent req="schema:{blocks:{type:\"resource\"  label_names:\"type\"  label_names:\"name\"  body:{attributes:{name:\"tags\"}}}}  option:{module_ctx:MODULE_CTX_TYPE_SELF  hint:{resource_type:\"aws_instance\"}}"
1 issue(s) found:

Error: instance type is t2.micro (aws_instance_example_type)

  on template.tf line 2:
   2:   instance_type = "t2.micro"

15:18:12 [DEBUG] runtime/asm_amd64.s:1571: tflint-ruleset-testing: 15:18:12 [TRACE] interceptor/logging.go:15: gRPC request: direction=host2plugin method=/plugin.GRPCController/Shutdown req=
15:18:12 [DEBUG] runtime/asm_amd64.s:1571: stdio: received EOF, stopping recv loop: err="rpc error: code = Unavailable desc = error reading from server: read unix @->/tmp/plugin3188026334: read: connection reset by peer"
15:18:12 [INFO]  runtime/asm_amd64.s:1571: plugin process exited: path=/home/codespace/.tflint.d/plugins/tflint-ruleset-testing pid=32007
15:18:12 [DEBUG] plugin/plugin.go:26: plugin exited

--loglevel

% cd integrationtest/inspection/basic
% tflint --loglevel trace
15:20:39 config.go:115: [INFO] Load config: .tflint.hcl
15:20:39 config.go:242: [DEBUG] Config loaded
15:20:39 config.go:243: [DEBUG]   Module: false
15:20:39 config.go:244: [DEBUG]   Force: false
15:20:39 config.go:245: [DEBUG]   IgnoreModules:
15:20:39 config.go:249: [DEBUG]   Varfiles:
15:20:39 config.go:250: [DEBUG]   Variables:

...<snip>...

15:20:39 provider.go:92: [INFO]   5 default rules enabled
15:20:39 terraform_deprecated_interpolation.go:48: [TRACE] Check `terraform_deprecated_interpolation` rule for `root` runner
15:20:39 terraform_empty_list_equality.go:46: [TRACE] Check `terraform_empty_list_equality` rule for `root` runner
15:20:39 terraform_module_pinned_source.go:61: [TRACE] Check `terraform_module_pinned_source` rule for `root` runner
15:20:39 terraform_module_version.go:58: [TRACE] Check `terraform_module_version` rule for `root` runner
15:20:39 terraform_workspace_remote.go:50: [TRACE] Check `terraform_workspace_remote` rule for `root` runner
15:20:39 runner.go:424: [INFO] template.tf:7,19-29 (aws_instance_example_type) is ignored by annotation:aws_instance_example_type (template.tf:6,3-7,1)
1 issue(s) found:

Error: instance type is t2.micro (aws_instance_example_type)

  on template.tf line 2:
   2:   instance_type = "t2.micro"

I don't know why there is this difference, but I think it's better in a term of maintainability to simply remove the option, as mentioned in #1070.