[py] disable overlay scrollbars when running tests with WebKitGTK+
[py] disable overlay scrollbars when running tests with WebKitGTK+

Some tests scroll to elements that keep them at the bottom of the
browser window. When attempting to click on them, the overlay scrollbar
receives the click instead.

joshbruning/selenium,SeleniumHQ/selenium,asolntsev/selenium,markodolancic/selenium,krmahadevan/selenium,Tom-Trumper/selenium,5hawnknight/selenium,valfirst/selenium,Ardesco/selenium,oddui/selenium,markodolancic/selenium,joshbruning/selenium,lmtierney/selenium,GorK-ChO/selenium,titusfortner/selenium,joshmgrant/selenium,asashour/selenium,mach6/selenium,asolntsev/selenium,Tom-Trumper/selenium,HtmlUnit/selenium,valfirst/selenium,davehunt/selenium,asashour/selenium,mach6/selenium,jabbrwcky/selenium,GorK-ChO/selenium,valfirst/selenium,lmtierney/selenium,jabbrwcky/selenium,lmtierney/selenium,davehunt/selenium,Ardesco/selenium,twalpole/selenium,jsakamoto/selenium,Dude-X/selenium,krmahadevan/selenium,joshmgrant/selenium,Tom-Trumper/selenium,chrisblock/selenium,asolntsev/selenium,Ardesco/selenium,mach6/selenium,GorK-ChO/selenium,krmahadevan/selenium,mach6/selenium,joshbruning/selenium,markodolancic/selenium,titusfortner/selenium,GorK-ChO/selenium,jsakamoto/selenium,asolntsev/selenium,asashour/selenium,Dude-X/selenium,juangj/selenium,asolntsev/selenium,krmahadevan/selenium,5hawnknight/selenium,asolntsev/selenium,asolntsev/selenium,titusfortner/selenium,markodolancic/selenium,lmtierney/selenium,markodolancic/selenium,asashour/selenium,5hawnknight/selenium,GorK-ChO/selenium,jabbrwcky/selenium,SeleniumHQ/selenium,HtmlUnit/selenium,jsakamoto/selenium,twalpole/selenium,titusfortner/selenium,jabbrwcky/selenium,chrisblock/selenium,Tom-Trumper/selenium,titusfortner/selenium,GorK-ChO/selenium,joshmgrant/selenium,krmahadevan/selenium,titusfortner/selenium,joshmgrant/selenium,joshmgrant/selenium,markodolancic/selenium,5hawnknight/selenium,krmahadevan/selenium,valfirst/selenium,davehunt/selenium,Tom-Trumper/selenium,Dude-X/selenium,oddui/selenium,markodolancic/selenium,joshmgrant/selenium,jabbrwcky/selenium,jabbrwcky/selenium,titusfortner/selenium,krmahadevan/selenium,5hawnknight/selenium,HtmlUnit/selenium,Dude-X/selenium,Ardesco/selenium,titusfortner/selenium,joshmgrant/selenium,Dude-X/selenium,davehunt/selenium,SeleniumHQ/selenium,jsakamoto/selenium,Dude-X/selenium,davehunt/selenium,joshbruning/selenium,juangj/selenium,Ardesco/selenium,twalpole/selenium,lmtierney/selenium,HtmlUnit/selenium,HtmlUnit/selenium,twalpole/selenium,valfirst/selenium,Ardesco/selenium,Tom-Trumper/selenium,jsakamoto/selenium,SeleniumHQ/selenium,markodolancic/selenium,juangj/selenium,oddui/selenium,davehunt/selenium,joshbruning/selenium,juangj/selenium,Ardesco/selenium,joshbruning/selenium,SeleniumHQ/selenium,twalpole/selenium,lmtierney/selenium,Ardesco/selenium,SeleniumHQ/selenium,twalpole/selenium,titusfortner/selenium,krmahadevan/selenium,SeleniumHQ/selenium,chrisblock/selenium,mach6/selenium,juangj/selenium,joshbruning/selenium,HtmlUnit/selenium,joshmgrant/selenium,jsakamoto/selenium,jsakamoto/selenium,chrisblock/selenium,oddui/selenium,valfirst/selenium,asashour/selenium,oddui/selenium,davehunt/selenium,oddui/selenium,lmtierney/selenium,jabbrwcky/selenium,5hawnknight/selenium,joshmgrant/selenium,Dude-X/selenium,oddui/selenium,joshmgrant/selenium,juangj/selenium,asashour/selenium,joshbruning/selenium,mach6/selenium,juangj/selenium,Tom-Trumper/selenium,jsakamoto/selenium,GorK-ChO/selenium,5hawnknight/selenium,valfirst/selenium,jabbrwcky/selenium,davehunt/selenium,Tom-Trumper/selenium,asolntsev/selenium,Dude-X/selenium,joshmgrant/selenium,markodolancic/selenium,lmtierney/selenium,asashour/selenium,5hawnknight/selenium,asashour/selenium,chrisblock/selenium,twalpole/selenium,davehunt/selenium,GorK-ChO/selenium,juangj/selenium,SeleniumHQ/selenium,mach6/selenium,titusfortner/selenium,mach6/selenium,asolntsev/selenium,chrisblock/selenium,jsakamoto/selenium,SeleniumHQ/selenium,chrisblock/selenium,chrisblock/selenium,SeleniumHQ/selenium,5hawnknight/selenium,jabbrwcky/selenium,juangj/selenium,GorK-ChO/selenium,twalpole/selenium,chrisblock/selenium,mach6/selenium,oddui/selenium,krmahadevan/selenium,joshbruning/selenium,SeleniumHQ/selenium,valfirst/selenium,HtmlUnit/selenium,HtmlUnit/selenium,titusfortner/selenium,valfirst/selenium,HtmlUnit/selenium,lmtierney/selenium,asashour/selenium,twalpole/selenium,HtmlUnit/selenium,valfirst/selenium,oddui/selenium,Ardesco/selenium,valfirst/selenium,Tom-Trumper/selenium,Dude-X/selenium