Update keymaster_tests for unique ID generation

Commit e104f386b29d ("Improve UNIQUE_ID generation",
http://aosp/I3eb8cf22cf52a6d5c7a085ae497500800ecd5438) forgot
to update the unit tests to match.

While in there, replace manual string lengths with use of strlen()
and .data_length.

Bug: 204598638
Bug: 204598638
Test: keymaster_tests
Change-Id: I59f3f0c42b59e255346f68199fc9a4a9ed113818
1 file changed