Differentiate between ep_perfsuite bucket types

Currently, the ep_perfsuite can run on two bucket types (persistent and ephemeral) based on the configuration supplied to engine_testapp. However, the generated reports do not differentiate between these two types, meaning you cannot tell which bucket type the tests were run on.

The generated reports should include the bucket type in the testsuite name, to enable CBNT to differentiate between these tests and properly identify regressions.