Store VPP API manifest files in a directory (vpp-api-files).
These files will contain a Whitelist file as well as API
CRC manifest file. At startup, the vpp-agent will check if the
API signature is compatible with the installed VPP. At runtime,
only API calls listed in the white list will be allowed.
Closes-Bug: #1855750
Change-Id: Idc37ef9b1cc10d08f606cb4b50b15f5f2932a050