Explicitly clear PoolManager by using context manager
Explicitly clear PoolManager by using context manager

Fixes #6878

This is meant to solve ResourceWarning messages when WebDrivers are instanced with a KeepAlive=False.

asolntsev/selenium,asolntsev/selenium,HtmlUnit/selenium,Ardesco/selenium,valfirst/selenium,SeleniumHQ/selenium,Dude-X/selenium,HtmlUnit/selenium,joshmgrant/selenium,Ardesco/selenium,valfirst/selenium,Dude-X/selenium,titusfortner/selenium,Ardesco/selenium,HtmlUnit/selenium,joshmgrant/selenium,SeleniumHQ/selenium,titusfortner/selenium,joshmgrant/selenium,Dude-X/selenium,titusfortner/selenium,HtmlUnit/selenium,SeleniumHQ/selenium,HtmlUnit/selenium,SeleniumHQ/selenium,titusfortner/selenium,valfirst/selenium,SeleniumHQ/selenium,asolntsev/selenium,SeleniumHQ/selenium,joshmgrant/selenium,SeleniumHQ/selenium,HtmlUnit/selenium,HtmlUnit/selenium,valfirst/selenium,asolntsev/selenium,Dude-X/selenium,joshmgrant/selenium,asolntsev/selenium,SeleniumHQ/selenium,Dude-X/selenium,joshmgrant/selenium,Ardesco/selenium,asolntsev/selenium,HtmlUnit/selenium,Ardesco/selenium,titusfortner/selenium,valfirst/selenium,SeleniumHQ/selenium,Ardesco/selenium,HtmlUnit/selenium,joshmgrant/selenium,Dude-X/selenium,valfirst/selenium,titusfortner/selenium,joshmgrant/selenium,titusfortner/selenium,valfirst/selenium,valfirst/selenium,SeleniumHQ/selenium,titusfortner/selenium,SeleniumHQ/selenium,valfirst/selenium,titusfortner/selenium,asolntsev/selenium,joshmgrant/selenium,Ardesco/selenium,Dude-X/selenium,titusfortner/selenium,valfirst/selenium,asolntsev/selenium,Ardesco/selenium,Dude-X/selenium,Ardesco/selenium,joshmgrant/selenium,joshmgrant/selenium,HtmlUnit/selenium,Dude-X/selenium,asolntsev/selenium,titusfortner/selenium,valfirst/selenium