qa/986 and the dmcache pmda

["Ken McDonell" <kenj@xxxxxxxxxxxxxxxx>]

All metrics from the dmcache pmda are returning Resource temporarily
unavailable.

And the pmda's log file contains ...

Traceback (most recent call last):
  File "/var/lib/pcp/pmdas/dmcache/pmdadmcache.python", line 208, in
dmcache_refresh
    self.caches[name] = DmCacheStats(line)  # extract stats values
  File "/var/lib/pcp/pmdas/dmcache/pmdadmcache.python", line 48, in __init__
    self.parse(text)
  File "/var/lib/pcp/pmdas/dmcache/pmdadmcache.python", line 61, in parse
    mbsize = long(data[4]) * 512        # metadata block size (from sectors)
IndexError: list index out of range

This is on a Debian 3.2.0 kernel, where dm-cache does not appear to be an
available kernel module

$ sudo modprobe dm-cache
FATAL: Module dm-cache not found.

and there is no "notrun" guard in this QA test and the test does not set
$DM_STATUS.