cert-request: accept CSRs with extraneous data
    
    The cert-request command used to accept CSRs that had extra data
    surrounding the PEM data, e.g. commentary about the contents of the
    CSR.  Recent commits that switch to using python-cryptography for
    cert and CSR handling broke this.  Our acceptance tests use such
    CSRs, hence the tests are now failing.
    
    To avoid the issue, freshly encode the python-cryptography
    CertificateSigningRequest object as PEM.  This avoids re-using the
    user-supplied data, in case it has extraneous data.
    
    Fixes: https://fedorahosted.org/freeipa/ticket/6472
    Reviewed-By: Martin Babinsky <mbabinsk@redhat.com>