cmd: Simplify recursive init outputs

[wata727]

Follow up of #2150

The strings.Builder-based approach is complicated to implement, so we'll change it to a simpler output.

without --recursive

Installed

No changes

Already installed

Before

$ tflint --init
Plugin "aws" is already installed
Plugin "google" is already installed

After

$ tflint --init
All plugins are already installed

with --recursive

Installed

Before

Installing plugins on each working directory...

====================================================
working directory: .

No plugins to install
====================================================
working directory: subdir

Installing "aws" plugin...
Installed "aws" (source: github.com/terraform-linters/tflint-ruleset-aws, version: 0.34.0)
====================================================
working directory: subdir2

Installing "google" plugin...
Installed "google" (source: github.com/terraform-linters/tflint-ruleset-google, version: 0.30.0)

After

$ tflint --recursive --init
Installing "aws" plugin in subdir...
Installed "aws" (source: github.com/terraform-linters/tflint-ruleset-aws, version: 0.34.0)
Installing "google" plugin in subdir2...
Installed "google" (source: github.com/terraform-linters/tflint-ruleset-google, version: 0.30.0)

Already installed

Before

Installing plugins on each working directory...

====================================================
working directory: .

No plugins to install
====================================================
working directory: subdir

Plugin "aws" is already installed
====================================================
working directory: subdir2

Plugin "google" is already installed

After

$ tflint --recursive --init
All plugins are already installed