Set is_exclusive for all ZFS test programs
Most ZFS tests create one or more pools using the same set of disks, so they
must have exclusive access to those disks. Tests that only use file-backed
vdevs and use no other global resources could in theory run in parallel. Also,
a few negative tests like zdb_001_neg could theoretically run in parallel. But
there's no way to set is_exclusive on a single test case; it can only be set
for an entire test program. So set it everywhere.
Sponsored by: Spectra Logic Corp