hdf5_der

[svn-r28321] SWMR-26: make check-vfd runs for a long time
The problem is in test/dsets which infinite looped when HDF5_DRIVER is "sec2" because
it had a for loop using a bool
type variable (compress) but the loop tried to increment to a third value. Changed the
type of compress to int allows the loop to run properly.

Secondly, the resas why it did not infinite loop when not in check-vfd is because the
getenv(HDF5_DRIVER) mistakenly assign driver as "nomatch" if it is not defined.
dsets skipped the test because "nomatch" is not one of the supported driver.
Fixed the code to assign "sec2" if $HDF5_DRIVER is not defined.

Tested: kituo, ostrich, osx1010dev