Fix javadoc error "class file for sun.util.resources.OpenListResourceBundle not found"

It seems to be a javac/javadoc bug.
See https://code.google.com/p/doclava/issues/detail?id=38

sun.util.resources.OpenListResourceBundle is a class defined in the host rt.jar,
but sometimes on some platform javadoc/javac can't find it.
-XDignore.symbol.file tells javadoc/javac to skip the stubs file ct.sym
and link against rt.jar directly.

Change-Id: I3930f7399fc14b2d6b43c29f737fa90f37515aff