Updated badges on README page
Updated badges on README page

Details:

* Switched PyPI version badge from img.shields.io to badge.fury.io due to
  continued bad performance and missing responses on img.shields.io.

* Switched Coveralls result badge from img.shields.io to coveralls.io itself
  for the same reason.

* Shortened the alternate text.

Signed-off-by: Andreas Maier <0903150dae73adcf31eccfd2633bf70bbc40bd52@gmx.de>

pywbem/pywbemtools,pywbem/pywbemtools