Bug 1321092

This bug is created as a clone of upstream ticket:
https://fedorahosted.org/freeipa/ticket/5720

If there are multiple versions of the same certificate (e.g. before and after renewal) coming from the same or different sources (CA certificates installed in IPA, user-provided certificates, etc.), some installers may fail with NSS error. This has been observed for `ipa-replica-prepare` ([https://www.redhat.com/archives/freeipa-users/2015-April/msg00189.html link]), but other installers are affected as well:
{{{
ipa.ipaserver.install.ipa_replica_prepare.ReplicaPrepare: DEBUG:   File "/usr/lib/python2.7/site-packages/ipapython/admintool.py", line 169, in execute
    self.ask_for_options()
  File "/usr/lib/python2.7/site-packages/ipaserver/install/ipa_replica_prepare.py", line 276, in ask_for_options
    options.http_cert_name)
  File "/usr/lib/python2.7/site-packages/ipaserver/install/ipa_replica_prepare.py", line 176, in load_pkcs12
    host_name=self.replica_fqdn)
  File "/usr/lib/python2.7/site-packages/ipaserver/install/installutils.py", line 785, in load_pkcs12
    nss_cert = x509.load_certificate(cert, x509.DER)
  File "/usr/lib/python2.7/site-packages/ipalib/x509.py", line 128, in load_certificate
    return nss.Certificate(buffer(data))

ipa.ipaserver.install.ipa_replica_prepare.ReplicaPrepare: DEBUG: The ipa-replica-prepare command failed, exception: NSPRError: (SEC_ERROR_LIBRARY_FAILURE) security library failure.
ipa.ipaserver.install.ipa_replica_prepare.ReplicaPrepare: ERROR: (SEC_ERROR_LIBRARY_FAILURE) security library failure.
}}}

This happens because we sometimes use `certutil -L -n -r` to get a DER-encoded certificate from a NSS database, and when there are multiple versions of that certificate, `certutil` returns the corresponding DER blobs concatenated, which other components are then unable to parse.