SERVER-13391 Rename slowNightly -> noPassthroughWithMongod and slowWeekly -> noPassthrough

This better represents their purpose and the difference between them.
SERVER-13391 Move slowest tests from noPassthrough* (formerly slow{Weekly,Nightly}) to slow*

slow1 and slow2 are new suites to hold very slow tests. The idea is that we
can create slow3, slow4, etc to keep the time to run the longest suite down.