add UDF file format reader to support solutions add-on installation

[vmanasiev]

Short Description

An internal package to support installation of VCD Solution Add-ons

Description

In this package a reader is implemented that supports extracting files from solutions add-on ISO without unpacking/mounting it advance.

Motivation

A new feature is being implemented where the vcd client and terraform provider should support installation of the VCD solution add-ons. Solution add-ons are packaged as an ISO media. To support larger files and avoid other issues with simple CDROM file format, the .iso file is packaged as UDF filesystem (specification: http://www.osta.org/specs/pdf/udf260.pdf ).
udf internal package implements partially that specification and enables read. Specifically, the code allows only reading of top level objects within a .ISO file.

[lvirbalas]

Thank you for your contribution. Approving in advance with a few requests below:

@vmanasiev or @dataclouder please add a few things:

1. Amend the PR description to state that this code is extracting only files from the top of the ISO tree.
2. Add top-level comment/description to the .go files (which are missing it) to explain the purpose and expectations of the code of a particular file.

[dataclouder]

Thank you for your contribution. Approving in advance with a few requests below:

@vmanasiev or @dataclouder please add a few things:

1. Amend the PR description to state that this code is extracting only files from the top of the ISO tree.

2. Add top-level comment/description to the .go files (which are missing it) to explain the purpose and expectations of the code of a particular file.

I will take care of the code description after merging.