Skip connection-timeout test on minix3.

Minix 3's Unix domain sockets don't seem to work the way we expect, so
skip connection-timeout test on that platform.  While there, group
together all similarly skipped tests and explicitly comment.

Author: daztucker

.github/configs

@@ -246,12 +246,14 @@ case "${TARGET_HOST}" in
 	# Also, Minix seems to be very limited in the number of select()
 	# calls that can be operating concurrently, so prune additional tests for that.
 	T="addrmatch agent-restrict brokenkeys cfgmatch cfgmatchlisten cfgparse
-	    connect connect-uri dynamic-forward
-	    exit-status forward-control forwarding hostkey-agent
-	    key-options keyscan knownhosts-command login-timeout multiplex
+	    connect connect-uri exit-status forwarding hostkey-agent
+	    key-options keyscan knownhosts-command login-timeout
 	    reconfigure reexec rekey scp scp-uri scp3 sftp sftp-badcmds
 	    sftp-batch sftp-cmds sftp-glob sftp-perm sftp-uri stderr-data
 	    transfer"
+	# Unix domain sockets don't work quite like we expect, so also skip any tests
+	# that use multiplexing.
+	T="$T connection-timeout dynamic-forward forward-control multiplex"
 	SKIP_LTESTS="$(echo $T)"
 	TEST_TARGET=t-exec
 	SUDO=""