Feature/no known hosts (#181)

* add "if_key_exists"

* add test

* fix flag

* fix SSH connection commands

* add test for if_key_exists=ignore

* add test for if_key_exists=fail

* add tests to Windows / macOS

* update CHANGELOG

* update badges

* update README

* fix README

* update README

* test no_known_hosts parameter

* implement

* ignore known_hosts if no_known_hosts is true

* refactor

* no_known_hosts is false

* Revert "no_known_hosts is false"

This reverts commit 206d310c5c.

* test on Windows / macOS

* test on Docker containers

* add tests for Docker containers

* test no_known_hosts parameter

* implement

* ignore known_hosts if no_known_hosts is true

* refactor

* no_known_hosts is false

* Revert "no_known_hosts is false"

This reverts commit 206d310c5c.

* test on Windows / macOS

* test on Docker containers

* use `known_hosts: no` instead of `no_known_hosts: true`

* update README

* update README

* "known_hosts: no" -> "known_hosts: unnecessary"

* update README

* update README

* update CHANGELOG

.github/workflows/verify-on-ubuntu.yml

@@ -257,3 +257,24 @@ jobs:
       run: ls -l ~/.ssh
     - name: git clone through SSH
       run: git clone git@github.com:shimataro/ssh-key-action.git tmp
+
+  known_hosts-unnecessary:
+    name: without known_hosts file
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+        - ubuntu-16.04
+        - ubuntu-18.04
+        - ubuntu-20.04
+    steps:
+    - name: Checkout source codes
+      uses: actions/checkout@v2
+    - name: Install SSH key
+      uses: ./.
+      with:
+        key: ${{ secrets.SSH_KEY_PEM }}
+        known_hosts: unnecessary
+    - name: print created files
+      run: ls -l ~/.ssh