fetch/wget: Add latest_versionstring method

Being able to query whether updated versions of a url are available
is useful, not least for the package reporting system. Since such code
is closely linked to the url type and the url itself, the fetcher
makes a locical place to contain this code.

For wget based urls this means taking upstream directory listings
and searching those for later versions, returning those that are
found.

The patch also adds unittests for this function so that if
improvements are made, the original test urls can be used
to evaulate the those changes.

This is based on code from Irina Patru <irina.patru@intel.com>.

Signed-off-by: Aníbal Limón <anibal.limon@linux.intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
progressbar: use '/usr/bin/env' in shebangs with python

To support yocto on systems with python3 as default version, scripts
should use /usr/bin/env python in the shebang, as this allows the use of
a fake env to mimic python2 as default version.

This patch simply replaces occurrences of #!/usr/bin/python with
 #!/usr/bin/env python and was done with this oneliner:

     git grep -lE '^#!/usr/bin/python' | xargs \
         sed -i 's|/usr/bin/python|/usr/bin/env python|'

Signed-off-by: Martin Hundebøll <martin@hundeboll.net>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>