Signed-off-by: NJiri Denemark <jdenemar@redhat.com>

The code for extracting sub-mounts would just do a STRPREFIX
check on the mount. This was flawed because if there were
the following mounts

 /etc/aliases
 /etc/aliases.db

and '/etc/aliases' was asked for, it would return both even
though the latter isn't a sub-mount.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

Move the code for lxcContainerGetSubtree into the virfile
module creating 2 new functions

  int virFileGetMountSubtree(const char *mtabpath,
                             const char *prefix,
                             char ***mountsret,
                             size_t *nmountsret);
  int virFileGetMountReverseSubtree(const char *mtabpath,
                                    const char *prefix,
                                    char ***mountsret,
                                    size_t *nmountsret);

Add a new virfiletest.c test case to validate the new code.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>