pio_unit_test fails during print

The pio_unit_test sometimes fails on the print statement,

```
Program received signal SIGFPE: Floating-point exception - erroneous arithmetic operation.

Backtrace for this error:
#0 0x7faf7e1becaf in ???
#1 0x7faf7fa00746 in write_float
at ../../../libgfortran/io/write_float.def:1276
#2 0x7faf7fa03bee in list_formatted_write_scalar
at ../../../libgfortran/io/write.c:1546
#3 0x40bfd6 in __ncdf_tests_MOD_test_nc4
at /sandbox/jenkins-ci/workspace/ParallelIO_LSan_cdash/src/tests/unit/ncdf_tests.F90:345
#4 0x40b3cc in pio_unit_test_driver
at /sandbox/jenkins-ci/workspace/ParallelIO_LSan_cdash/src/tests/unit/driver.F90:184
#5 0x40b75a in main
at /sandbox/jenkins-ci/workspace/ParallelIO_LSan_cdash/src/tests/unit/driver.F90:7
```

The code that prints values is

```
! Check the settings of the chunk cache for netCDF-4/HDF5 files.
print*, 'testing PIO_get_chunk_cache'
ret_val = PIO_get_chunk_cache(pio_iosystem%iosysid, iotype, chunk_cache_size_in, &
chunk_cache_nelems_in, chunk_cache_preemption_in)
print*, 'PIO_get_chunk_cache returned ', chunk_cache_size_in, &
chunk_cache_nelems_in, chunk_cache_preemption_in
```