docs: update long descriptions for test, e2e and lint

Closes #12930

Author: alan-agius4

packages/angular/cli/commands/e2e-long.md

@@ -1,2 +1,2 @@
 Must be executed from within a workspace directory.
-When a project name is not supplied, the configured default e2e project of the workspace is used.
+When a project name is not supplied, it will execute for all projects.

packages/angular/cli/commands/lint-long.md

@@ -1,4 +1,4 @@
 Takes the name of the project, as specified in the  `projects` section of the `angular.json` workspace configuration file.
-When a project name is not supplied, uses the configured `defaultProject` of the workspace.
+When a project name is not supplied, it will execute for all projects.
 
 The default linting tool is [TSLint](https://palantir.github.io/tslint/), and the default configuration is specified in the project's `tslint.json` file.

packages/angular/cli/commands/test-long.md

@@ -0,0 +1,2 @@
+Takes the name of the project, as specified in the `projects` section of the `angular.json` workspace configuration file.
+When a project name is not supplied, it will execute for all projects.

packages/angular/cli/commands/test.json

@@ -2,7 +2,7 @@
   "$schema": "http://json-schema.org/schema",
   "$id": "ng-cli://commands/test.json",
   "description": "Runs unit tests in a project.",
-  "$longDescription": "",
+  "$longDescription": "./test-long.md",
 
   "$aliases": [ "t" ],
   "$scope": "in",