Disable zpool_upgrade_002_pos test case

This test case frequently triggers issue #4034. There exists a
fix for this which is in the process of being upstreamed. Until
that fix is available disable the test case.

Reviewed by: George Wilson <george.wilson@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #5329
Issue #4034