src/test/ssl/t/001_ssltests.pl should not tromp on file permissions

I got tripped up while building the 10beta1 tarballs by the fact
that src/test/ssl/ssl/client.key had permissions 0600 in my git
checkout.  After a fair amount of head-scratching, I figured out
that this must have been a side-effect of having run the SSL regression
tests at some point in the past.  I do not like test scripts that
scribble on non-transient files, not even (or perhaps especially not)
if they're "just" changing the permissions.

We could maybe make 001_ssltests.pl save and restore the file's
permissions, but I think probably a cleaner answer is to have it
make a temporary copy and set the permissions on that.

Thoughts?

			regards, tom lane