Fix compiler warnings: PRIu64 is the proper way to output uint64_t
values.  See https://svn.open-mpi.org/trac/ompi/wiki/PrintfCodes.
Cleanup the sensor framework close - existing code was using incorrect object type. Don't start sensors if sample rate is zero. Don't add zero-byte data from resusage as it means nothing was measured.

cmr=v1.7.4:reviewer=hjelmn