Fix interaction between --only and defaults

We should treat defaults specially, and even when `--only` is
specified, we should always run defaults.

dotbot/dispatcher.py

@@ -22,8 +22,9 @@ class Dispatcher(object):
         success = True
         for task in tasks:
             for action in task:
-                if self._only is not None and action not in self._only \
-                        or self._skip is not None and action in self._skip:
+                if (self._only is not None and action not in self._only \
+                        or self._skip is not None and action in self._skip) \
+                        and action != 'defaults':
                     self._log.info('Skipping action %s' % action)
                     continue
                 handled = False

test/Vagrantfile

@@ -1,7 +1,6 @@
 Vagrant.configure(2) do |config|
   config.vm.box = 'ubuntu/bionic64'
 
-  # sync by copying for isolation
   config.vm.synced_folder "..", "/dotbot", mount_options: ["ro"]
 
   # disable default synced folder

test/tests/only-defaults.bash

@@ -0,0 +1,21 @@
+test_description='--only does not skip defaults'
+. '../test-lib.bash'
+
+test_expect_success 'setup' '
+echo "apple" > ${DOTFILES}/x
+'
+
+test_expect_success 'run' '
+run_dotbot --only link <<EOF
+- defaults:
+    link:
+      create: true
+- shell:
+  - echo "pear" > ~/z
+- link:
+    ~/d/x: x
+'
+
+test_expect_success 'test' '
+grep "apple" ~/d/x && ! test -f ~/z
+'