[MGPG-92] `--pinentry-mode error` cannot be used with gpg-agent "extra" socket

**[Nick Dimiduk](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=ndimiduk)** opened **[MGPG-92](https://issues.apache.org/jira/browse/MGPG-92?redirect=false)** and commented

Over on HBA[SE-27312](https://issues.apache.org/jira/browse/SE-27312), we found an issue in our release automation, which relies on using this plugin and a GnuPG agent for performing builds inside of an isolated environment. With GPG version >= 2.1, the plugin will make use of `--pinentry-mode error`. This feature appears to not be available using the "extra" gpg-agent socket. We had to "upgrade" to using the "standard" socket, which probably exposes more gpg features to the isolated environment than we would like.

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**Issue Links:**
- [HBASE-27312](https://issues.apache.org/jira/browse/HBASE-27312) Update create-release to work with maven-gpg-plugin-3.0.1 and gnupg >= 2.1.x

Start with the plugin's GnuPG invocation and investigate how `--pinentry-mode error` is handled when using the gpg-agent "extra" socket. Reproduce the reported failure with GnuPG >= 2.1 and determine what behavior should allow isolated release builds to use the extra socket without exposing the standard socket.

Written by the indexing model from the issue text.