Disable zvol_ENOSPC_001_pos on 32-bit systems

Occasionally observed failure of zvol_ENOSPC_001_pos due to the
test case taking too long to complete.  Disable the test case until
it can be improved.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #5848 
Closes #6862

tests/zfs-tests/tests/functional/zvol/zvol_ENOSPC/zvol_ENOSPC_001_pos.ksh

@@ -47,6 +47,11 @@
 
 verify_runnable "global"
 
+# See issue: https://github.com/zfsonlinux/zfs/issues/5848
+if is_32bit; then
+	log_unsupported "Test case runs slowly on 32 bit"
+fi
+
 function cleanup
 {
 	rm -rf $TESTDIR/*