Fix log test to work on other people's timezones.

Oops.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Remove a test leak, and make suppressions file work on 32 bit and older valgrind.

Also, check that key is valid in helper.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>