jvpp: provide more detailed exception logs (VPP-436)

Error descriptions provided in api_errno.h are never used,
only error tag/name and number make it to enum vnet_api_error_t
so new macro is introduced in jvpp_common.c to extract message
according to error number and passed to VppCallbackException
constuctor.

Change-Id: If2a687752807d7250d9226987583df00f151e87f
Signed-off-by: Matej Perina <mperina@cisco.com>
Signed-off-by: Marek Gradzki <mgradzki@cisco.com>