Annotate hudson.Util methods.

The change adds annotations for all methods inside the class. The initial idea - enforce checks of symlink methods to prevent NPEs on Windows platforms.

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Fixed annotations in hudson/Util.java according to the discussion with @jglick and @kutzi

Signed-off-by: Oleg Nenashev <o.v.nenashev@gmail.com>
Merge pull request #1223 from synopsys-arc-oss/hudson_util_annotations

Annotate hudson.Util methods by @CheckForNull and @Nonnull