Use file-based pools for zpool_expand test 002 and enable it

Use file-based pools for zpool_expand test 002 and enable it

Use -pH flags in get_pool_prop so that numeric properties such as size
can be compared.  The zpool_expand test suite is currently the only one
which uses get_pool_prop for a numeric property.

Add TEMPFILE and TEMPFILE{0,1,2} to default.cfg for tests that must
build pools on top of files, such as this one where expansion is
necessary but the entries in DISKS may not point to entities that can be
expanded.

Base the pool used for testing on file-type VDEVs instead of using zvols
within an underlying pool, to avoid issues that come up when pools are
backed by other pools.

Remove shell variables EX_1GB and EX_2GB used to recognize correct expansion,
and instead calculate the appropriate values based on the variables used to
control file or volume size, org_size and exp_size.  This change is also
made in test 001 although that test is not enabled because it depends on
FMA.

Finally, enable zpool_expand_002_pos.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Don Brady <don.brady@intel.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Olaf Faaland <faaland1@llnl.gov>
Closes #5757