xapp-frame go imrpovements

xapp-frame go imrpovements

xapp registration error handling won't work fully
as it won't return error when status code in response
is wrong. This will stop app registeration retries.

Config file get rest functionality tries to read
config file from hard coded path, which is wrong assumtion.
xapp-frame reads config file given as argument "-f" or
from CFG_FILE env variable. Thou config file rest api
should try read file that is really used.

Signed-off-by: Juha Hyttinen <juha.hyttinen@nokia.com>
Change-Id: Ib5f4cce4cbad3a84c0c412c9b9b03f2cd69605ca