Force TTY mode for integration test logs

[pudelkoM]

This will force printing the timestamp, calling function and colors on local runs.
Since test output is not collected by any monitoring system, we can use a more human readable format.

This only affects local runs, GHA already attach a TTY.

[pudelkoM]

Some more testing made me confident that it's not a local issue:

docker run -it --rm -v $(pwd):$(pwd) -w $(pwd) golang
make test-bess-integration-native

without these changes results in the usual kv format:

time="2022-03-08T19:58:29Z" level=info msg="Removed connection to 127.0.0.1:48185"
time="2022-03-08T19:58:29Z" level=info msg="Done waiting for PFCPConn completions"
time="2022-03-08T19:58:29Z" level=info msg="Exit function Bess"
time="2022-03-08T19:58:29Z" level=info msg="Shutdown complete for 127.0.0.1:48185"
time="2022-03-08T19:58:29Z" level=info msg="Shutdown complete"

with the changes, it looks like this:

INFO[2022-03-08T20:00:14Z]/home/max/upf-epc/pfcpiface/node.go:145 github.com/omec-project/upf-epc/pfcpiface.(*PFCPNode).Serve() Removed connection to 127.0.0.1:40306
INFO[2022-03-08T20:00:14Z]/home/max/upf-epc/pfcpiface/node.go:149 github.com/omec-project/upf-epc/pfcpiface.(*PFCPNode).Serve() Done waiting for PFCPConn completions
INFO[2022-03-08T20:00:14Z]/home/max/upf-epc/pfcpiface/bess.go:193 github.com/omec-project/upf-epc/pfcpiface.(*bess).exit() Exit function Bess
INFO[2022-03-08T20:00:14Z]/home/max/upf-epc/pfcpiface/node.go:170 github.com/omec-project/upf-epc/pfcpiface.(*PFCPNode).Done() Shutdown complete

In logrus, having colors enabled changes the output format: sirupsen/logrus#1194