Added SHA256 test certificates

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.
diff --git a/tests/data_files/cli.opensslconf b/tests/data_files/cli.opensslconf
new file mode 100644
index 0000000..ae9ab9d
--- /dev/null
+++ b/tests/data_files/cli.opensslconf
@@ -0,0 +1,4 @@
+[cli-rsa]
+subjectKeyIdentifier=hash
+authorityKeyIdentifier=keyid:always,issuer:always
+basicConstraints = CA:false