add support for checkov for linting terraform files (#4006)

* add support for checkov for terraform

* add tests for checkov handler

* add basic linter config tests for checkov

* update supported tools and languages lists

* simplify ale_linters#terraform#checkov#Handle

* ensure "-o json --quiet" is always set for checkov

* add documentation for checkov including config options

* fix tests after changing handling of default options for checkov

* add checkov to list of tools in doc/ale.txt

doc/ale-supported-languages-and-tools.txt

@@ -560,6 +560,7 @@ Notes:
 * Tcl
   * `nagelfar`!!
 * Terraform
+  * `checkov`
   * `terraform`
   * `terraform-fmt-fixer`
   * `terraform-ls`

doc/ale-terraform.txt

@@ -2,6 +2,25 @@
 ALE Terraform Integration                               *ale-terraform-options*
 
 
+===============================================================================
+checkov                                                 *ale-terraform-checkov*
+
+g:ale_terraform_checkov_executable         *g:ale_terraform_checkov_executable*
+                                           *b:ale_terraform_checkov_executable*
+
+  Type: |String|
+  Default: `'checkov'`
+
+  This variable can be changed to use a different executable for checkov.
+
+
+g:ale_terraform_checkov_options               *g:ale_terraform_checkov_options*
+                                              *b:ale_terraform_checkov_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be changed to set additional options for checkov.
+
 ===============================================================================
 terraform-fmt-fixer                                   *ale-terraform-fmt-fixer*
 

doc/ale.txt

@@ -3112,6 +3112,7 @@ documented in additional help files.
   tcl.....................................|ale-tcl-options|
     nagelfar..............................|ale-tcl-nagelfar|
   terraform...............................|ale-terraform-options|
+    checkov...............................|ale-terraform-checkov|
     terraform-fmt-fixer...................|ale-terraform-fmt-fixer|
     terraform.............................|ale-terraform-terraform|
     terraform-ls..........................|ale-terraform-terraform-ls|