Use Java 7 Files API for IO instead of the older API

We should try to use the NIO Files API for file IO. The older file API causes issues on Windows, since it doesn't set the FILE_SHARE_DELETE flag when opening files. This causes Storm to be unable to delete files that have open handles, which is unlike the behavior on Linux. This can cause e.g. unnecessary supervisor crashes because one thread tries to delete a file that is open in another.

For the same reason, we should get rid of uses of common-io FileUtils, and get rid of uses of Guava's Files class that opens IO streams.