Warp: Reuse manager during whole test

Manager is created for each request independently:
https://github.com/arquillian/arquillian-extension-warp/blob/master/impl/src/main/java/org/jboss/arquillian/warp/filter/WarpFilter.java#L123

<aslak> Scopes a bound to ThreadLocals, so you'll need to 'reactivate' application scope pr request