Store ndkKnownLibs in the config

Storing ndkKnownLibs prevents multiple tests from running in parallel
as one may be writing to the list while another is reading from it.
Store it in the config so each test has its own copy.

Test: go test -race ./apex
Change-Id: Iba57c9494012c9e0ae9e5ffaa63b9b2bd2c77492