core: defined action hook names can be strings, convert to symbols

CHANGELOG.md

@@ -16,6 +16,8 @@ BUG FIXES:
     in the installer context. [GH-2231]
   - core: Clear `DYLD_LIBRARY_PATH` on Mac if the subprocess is executing
     a setuid or setgid script. [GH-2243]
+  - core: Defined action hook names can be strings now. They are converted
+    to symbols internally.
   - guests/debian: FQDN is properly set when setting the hostname. [GH-2254]
   - guests/linux: Fix poor chown command for mounting VirtualBox folders.
   - guests/linux: Don't raise exception right away if mounting fails, allow

lib/vagrant/plugin/v2/plugin.rb

@@ -73,7 +73,7 @@ module Vagrant
           # The name is currently not used but we want it for the future.
 
           hook_name ||= ALL_ACTIONS
-          components.action_hooks[hook_name] << block
+          components.action_hooks[hook_name.to_sym] << block
         end
 
         # Defines additional command line commands available by key. The key