Previously, 2048-bit and 4096-bit RSA key files had their bitsize indicated in their filename, while the original
1024-bit keys hadn't. This commit unifies the naming scheme by always indicating the bitsize in the filename.
This commit adds the commands used to generate the various RSA keys to tests/Makefile so that they can be easily
regenerated or modified, e.g. if larger key sizes or other encryption algorithms need to be tested in the future.
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.
