auth: Get correct viceid in legacy GetToken

auth: Get correct viceid in legacy GetToken

When ktc_GetTokenEx needs to get tokens via the legacy ktc_GetToken
interface, it was not extracting the viceid. Make it set the viceid so
the caller gets the correct id.

Normally this would require parsing the given client name. To reduce
the amount of times we store and extract the viced from the "AFS ID
%d" string, create a helper GetToken function that can store the
viceid directly, without storing it in a string.

Change-Id: Ib03a419aee6eaed3b253c4d5d575d4dd8d3b8ddc
Reviewed-on: http://gerrit.openafs.org/4482
Tested-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementix.org>