Exclude remote file systems from inspection of unmanaged files

Remote file systems are all file systems which are mounted either via NFS or
CIFS, directly or via the auto mounter. These file systems are not extracted
by the unmanaged-files inspector. The mount points of remote file systems are
stored as entry of type 'remote-dir' in the unmanaged-files scope in the
system description.
This might be a matter of taste and I'm not sure if Cornelius would agree, but personally I wouldn't test the private `parse_mounts` method. It's not part of the interface the class offers and thus shouldn't have to be tested separately.

My counter proposal would look like this:
```ruby
describe MountPoints do
  subject {
    system = System.new
    allow(system).to receive(:cat_file).with("/proc/mounts").
      and_return(File.open("spec/data/unmanaged_files/proc_mounts"))

    MountPoints.new(system)
  }

  describe "#all" do
    it "returns an array containing all mount points" do
      expect(subject.all).to match_array(["/",  "/data", "/dev", "/homes/tux"])
    end
  end

  describe "#remote" do
    it "returns an array containing the remote mount points" do
      expect(subject.remote).to match_array(["/homes/tux"])
    end
  end

  describe "#local" do
    it "returns an array containing the local mount points" do
      expect(subject.local).to match_array(["/", "/data"])
    end
  end
end
```

While writing this test I noticed that `/` is returned twice in `#all`, I suppose that's a bug, no?