tests: Add tests for afsconf_'s key functions

tests: Add tests for afsconf_'s key functions

Add tests for all of the public functions that afsconf exports
to manipulate KeyFiles. Include a sample Keyfile to start with, to
ensure that we can continue to read KeyFiles produced by current
versions of the code.

These tests are here to catch regressions with a forthcoming rewrite
of KeyFile handling.

Change-Id: I02aaff82aa7e1b7a73981c7cf26a81164e0dd932
Reviewed-on: http://gerrit.openafs.org/3598
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>