1) Rename the old shell tool "mysql_upgrade", to avoid a name collision.
2) Improve the spec file, to explicitly use a temporary socket.
scripts/mysql_upgrade_shell.sh:
Rename: scripts/mysql_upgrade.sh -> scripts/mysql_upgrade_shell.sh
scripts/Makefile.am:
The old shell script "mysql_upgrade" must be renamed,
so that its name does not collide with the new binary.
support-files/mysql.spec.sh:
The previous version was incomplete, as it did not cover the case
where the DBA had configured a non-default socket file.
Solve that by creating and explicitly providing a temporary directory
for the socket just for the duration of "mysql_upgrade", which also
can be better protected than the default socket.
