Ensure nsswitch.conf config for netgo

[yosifkit]

Alpine 3.16 has updated to include an nsswitch.conf. But we need to ensure 3.15 still works as well.

Step 1/10 : FROM alpine:3.15
Step 3/10 : RUN set -eux; 	if [ -e /etc/nsswitch.conf ]; then 		grep '^hosts: files dns' /etc/nsswitch.conf; 	else 		echo 'hosts: files dns' > /etc/nsswitch.conf; 	fi
 ---> Running in 79d0f913ddf7
+ '[' -e /etc/nsswitch.conf ]
+ echo 'hosts: files dns'

Step 1/10 : FROM alpine:3.16
...
Step 3/10 : RUN set -eux; 	if [ -e /etc/nsswitch.conf ]; then 		grep '^hosts: files dns' /etc/nsswitch.conf; 	else 		echo 'hosts: files dns' > /etc/nsswitch.conf; 	fi
 ---> Running in b9440f91dc03
+ '[' -e /etc/nsswitch.conf ]
+ grep '^hosts: files dns' /etc/nsswitch.conf

Related to docker-library/docker#384