tests: remove --provider from vagrant up commands

Vagrant is smart enough to detect what environment it is running in.
Rather than try to switch and provide the right provider name on each
platform, let's just let Vagrant detect it.

features/user_home_dir_mount.feature

@@ -15,14 +15,14 @@ Feature: Mount of user home directory
       end
     end
     """
-    When I successfully run `bundle exec vagrant up --provider <provider>`
-    Then stdout from "bundle exec vagrant up --provider <provider>" should contain "Installing SSHFS client..."
-    And  stdout from "bundle exec vagrant up --provider <provider>" should contain "Mounting SSHFS shared folder..."
-    And  stdout from "bundle exec vagrant up --provider <provider>" should contain "Folder Successfully Mounted!"
+    When I successfully run `bundle exec vagrant up`
+    Then stdout from "bundle exec vagrant up" should contain "Installing SSHFS client..."
+    And  stdout from "bundle exec vagrant up" should contain "Mounting SSHFS shared folder..."
+    And  stdout from "bundle exec vagrant up" should contain "Folder Successfully Mounted!"
     And user's home directory should be mounted
 
     Examples:
-      | box              | provider   |
-      | centos/7         | virtualbox |
+      | box      |
+      | centos/7 |