Fix bug using destructed fs_root to uninstall operations

 This commit temporary stops uninstalling operations
to avoid this bug.
Possible solution:
 * Manage fs_root using shared_ptr and pass fs_root
    managed by enable_shared_from_this to installers.
fs_root: remove operations using module name
Makefile: mount: make dependency to 'modules'
mod_net_dns: change log messages