mythtv-buildebuild.py updated to define python version to use

Update README:
Updated the README to create a two stage update approach by creating a symbolic link to update the git repository followed by building the ebuilds.
Note: This update assumes Gentoo alphabetically executes the files in /etc/portage/postsync.d/ .

Update mythtv-buildebuild.py:
Moved mythtv-buildebuild.py to mythtv-buildebuild.py2
Changed to required python2
Updated to respect the Portage variable DISTDIR in /etc/make.conf when saving the tarball.
Updated to use the actual file path rather than the file path of the symbolic link during execution and updated the opts.packages variables accordingly.

Added file mythtv-buildebuild.py3:
Includes the changes to mythtv-buildebuild.py, but it has been updated to use python3. Added functionality to reconnect upon failed github connections via try-exception methods.

TODO mythtv-buildebuild.py3: The urllib.request.urlopen( args).read.decode( 'encoding-type') really should be updated to check the headers to determine the proper web site encoding (i.e. latin1, ascii, utf-8, etc).