Fixed the record_wpr retry mechanism in webpages_playback.py.
Updated all page sets to remove the no longer needed RunSmoothness and RunNavigateSteps.
Updated the key_silk_cases pagesets to point to a non svn location:
* skia_fontwipe_desktop.py
* skia_silkfinance_desktop.py
Removed mercurynews, record_wpr was timing out because of a popup.
Added back the following pagesets which were previously disabled but are now working again:
* skia_cnn_nexus10.py
* skia_wordpress_desktop.py
* skia_transformice_nexus10.py
BUG=skia:3049
Review URL: https://codereview.chromium.org/684863002
