The code added to validate CA certificates did not take into
account the possibility that the cacert.pem file can contain
multiple (concatenated) cert data blocks. Extend the code for
loading CA certs to use the gnutls APIs for loading cert lists.
Add test cases to check that multi-level trees of certs will
validate correctly.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

Currently every test case in the TLS test suite generates the
certs fresh. This is a waste of time, since its parameters
don't change across test cases. Create certs once in main
method.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

The virnettlscontexttest.c tests both virNetTLSContext
and virNetTLSSession functionality. Split into two
separate tests, to make the code size more manageable
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>