Fixing bug 1032

This bugfix introduces the notion of symlink handling in the
FSMongo plugin. The change focus mainly in setting properly
the flags for a symlink file and store that metadata in an
adequate format in MongoDB.

Change-Id: I04ea122d3feed08762c38fa2557113ff2de35e3b
Signed-off-by: sousaedu <eduardo.sousa@canonical.com>