torture: Keep old-school dmesg format

This commit adds "#define pr_fmt(fmt) fmt" to the torture-test files
in order to keep the current dmesg format.  Once Joe's commits have
hit mainline, these definitions will be changed in order to automatically
generate the dmesg line prefix that the scripts expect.  This will have
the beneficial side-effect of allowing printk() formats to be used more
widely and of shortening some pr_*() lines.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Joe Perches <joe@perches.com>