Add 'vold' to Brillo manifest.

Fixes build breakage now that fs_mgr includes headers from vold.

default.xml

diff --git a/default.xml b/default.xml
index 16178ec..d470328 100644
--- a/default.xml
+++ b/default.xml
@@ -178,6 +178,7 @@
   <project path="system/tools/bpt" name="platform/system/tools/bpt" groups="bdk" />
   <project path="system/tpm" name="platform/system/tpm" groups="bdk" />
   <project path="system/update_engine" name="platform/system/update_engine" groups="bdk" />
+  <project path="system/vold" name="platform/system/vold" groups="bdk" />
   <project path="system/weaved" name="platform/system/weaved" groups="bdk" />
   <project path="system/webservd" name="platform/system/webservd" groups="bdk" />