test: Stop gpg-agent daemons that are started for the test framework's gpg key

They normally shutdown when the GNUPGHOME directory is deleted, but on
NFS they keep the directory from being deleted. And also, this avoids
a number of them piling up while the test suite is running.

doc/bugs/running_tests_on_NFS_HOME_does_not_exit_cleanly__58___gpgtmp.mdwn

@@ -24,3 +24,4 @@ so it seems to relate to gpg, and not unlikely to be out of git-annex control, b
 [[!meta author=yoh]]
 [[!tag projects/datalad]]
 
+> [[fixed|done]] --[[Joey]]

doc/bugs/running_tests_on_NFS_HOME_does_not_exit_cleanly__58___gpgtmp/comment_1_84a2d253843903f9811652b78d0fa7ba._comment

@@ -0,0 +1,25 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2020-08-28T17:17:07Z"
+ content="""
+This may depend on the version of gpg in use. With latest version, I see:
+
+	 374404 ?        Ss     0:00 gpg-agent --homedir /home/joey/src/git-annex/.t/tmprepo85/../gpgtmp/1 --use-standard-socket --daemon
+	 374411 ?        Ss     0:01 gpg-agent --homedir /home/joey/src/git-annex/.t/tmprepo85/../gpgtmp/2 --use-standard-socket --daemon
+
+12 of these build up by the end of the test suite. But here when the test suite
+exits, they all terminate.
+
+Presumably they have a deleted file they're holding open, which causes NFS to
+break in the ususal NFS way. Here they have an inotify handle, and some kind of
+socket. Based on the .nfs filename, which I think usually includes the name of
+the deleted file but here does not, I suspect it might be for the directory
+itself, and so due to the inotify handle.
+
+Ah, I think I see.. When I delete the directory, gpg-agent notices
+and exits.
+
+`gpgconf --kill all` can be used to stop them, so I've made the test
+suide do that after using gpg.
+"""]]