Do not assert if we fail to compose ssl_crtd request. Do blocking generation.

Do not assert if we fail to compose ssl_crtd request. Do blocking generation.

Users report assertions when OpenSSL fails to write a true server certificate
to to memory. Since that certificate is received from a 3rd party, we should
not assert that it is writeable. Besides, OpenSSL may have limitations/bugs
even if dealing with valid certificates.

If we fail to componse a request, we now try the good old blocking in-process
certificate generation.

Currently, it is not known what exactly causes OpenSSL to fail as we are
unable to trigger the assertion in a controlled test.