ACCUMULO-1628 Fixes issue after previous changes which interrupted a deep-copy

Pushes the interrupt flag from the SourceSwitchingIterator down to the
FileManager and InMemoryMap. This should avoid passing the interrupt
into a deep copy which isn't supported. Adds some more tests which
previously caused the edge case which is now fixed.

Signed-off-by: Josh Elser <elserj@apache.org>