For selection of test cases, see comments added in the commit.
It makes the most sense to test with chains using ECC only, so for the chain
of length 2 we use server10 -> int-ca3 -> int-ca2 and trust int-ca2 directly.
Note: server10.crt was created by copying server10_int3_int-ca2.crt and
manually truncating it to remove the intermediates. That base can now be used
to create derived certs (without or with a chain) in a programmatic way.
We have code to skip them but didn't have explicit tests ensuring they are
(the corresponding branch was never taken).
While at it, remove extra copy of the chain in server10*.crt, which was
duplicated for no reason.
With SHA-1 deprecation, we need a few certificates using algorithms in
the default support list. Most tests still use SHA-1 though.
The generation process for the new certificates is recorded in the makefile.
As we're about to change the chain construction logic, we want to make sure
the callback will still be called exactly when it should, and not on the
(upcoming) ignored certs in the chain.
