The virNetTLSContextNew was being passed key/cert parameters in
the wrong order. This wasn't immediately visible because if
virNetTLSContextNewPath was used, a second bug reversed the order
of those parameters again.

Only if the paths were manually specified in /etc/libvirt/libvirtd.conf
did the bug appear

* src/rpc/virnettlscontext.c: Fix order of params passed to
  virNetTLSContextNew

This provides two modules for handling TLS

 * virNetTLSContext provides the process-wide state, in particular
   all the x509 credentials, DH params and x509 whitelists
 * virNetTLSSession provides the per-connection state, ie the
   TLS session itself.

The virNetTLSContext provides APIs for validating a TLS session's
x509 credentials. The virNetTLSSession includes APIs for performing
the initial TLS handshake and sending/recving encrypted data

* src/Makefile.am: Add to libvirt-net-rpc.la
* src/rpc/virnettlscontext.c, src/rpc/virnettlscontext.h: Generic
  TLS handling code