With some libc impls (ie: Xcode 13.1), sprintf is marked as deprecated
and causes the build with `-Werror` to fail. Switch the `sprintf` usage
in test_nvs.cpp to use `snprintf` to allow builds to complete without
warning.
Host tests of nvs_flash eligible to run in Linux implementation of nvs flash were migrated. Remaining test cases
were left in original folder. Migrated test cases use CMake instead of make.