GnuPG intermittently fails to fetch pubkey from keyserver

[qrkourier]

When the hard-coded keyserver in docker-entrypoint.sh is not available or too slow then GnuPG will fail to fetch the needed pubkey and build will fail with "cannot assign address".

Here's a workaround to try several keyservers in turn that I found in another repo with the same issue.

[yosifkit]

My current opinion of this is expressed in docker-library/cassandra#131 (comment).

Related issues: docker-library/tomcat#87, docker-library/tomcat#108, #263 (comment), docker-library/httpd#66 (comment), docker-library/php#586, docker-library/postgres#443, MariaDB/mariadb-docker#108, docker-library/php#630, docker-library/python#280, docker-library/official-images#4252

[MichaelBrenden]

gnupg2 works better than gnupg