Touch attribute file to fix errors like:
Can't open ./demoCA/index.txt.attr for reading,
No such file or directory
140553384993216:error:02001002:system library:
fopen:No such file or directory:../crypto/bio/bss_file.c:72:
fopen('./demoCA/index.txt.attr','r')
140553384993216:error:2006D080:BIO routines:
BIO_new_file:no such file:../crypto/bio/bss_file.c:79:
Check that the request matches the signature
* fix CRL tests to work
* regenerate certificates to be at least 2048 bit
(fixes buster and rhel8 in buildbot)
* update generate-ssl-cert.sh to generate crl files
* make all SSL tests to use certificates generated
in generate-ssl-cert.sh, remove unused certificates
and make sure that private ca key is not deleted at the end of
the procedure, so that we could generate additional certificates
any time without regenerating everything
