init: Use std::string_view instead of std::string where appropriate

Slightly reduce the time that is required to start the init process by
changing two static std::string variables into std::string_view variables.

Change-Id: Ib683a603da5f3d8968b26453b12544fed8a6397f
Signed-off-by: Bart Van Assche <bvanassche@google.com>