Add okv function to the TAP test library

Add okv function to the TAP test library

Add an okv() varient of the ok() function that takes the arguments as
a va_list instead of as a variable argument list.  This makes it easier
to reuse ok() when writing other tests.

Change-Id: Icaeaaf9d6bd9d54bfd886a75961d98367ee0fb9a
Reviewed-on: http://gerrit.openafs.org/2098
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>