Pass virSecurityManagerPtr object further down into LXC setup code

Pass virSecurityManagerPtr object further down into LXC setup code

Currently the lxcContainerSetupMounts method uses the
virSecurityManagerPtr instance to obtain the mount options
string and then only passes the string down into methods
it calls. As functionality in LXC grows though, those
methods need to have direct access to the virSecurityManagerPtr
instance. So push the code down a level.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>