mds/MDSContext: debug log RTTI context class

Because otherwise on an assertion failure it's not obvious
what kind of Context we were handling when it went down.

Signed-off-by: John Spray <john.spray@redhat.com>
mds/Migrator: fix more contexts

Squash me!

Signed-off-by: John Spray <john.spray@redhat.com>
mds: fix broken context constructor

Squash me!

Signed-off-by: John Spray <john.spray@redhat.com>
mds/MDSContext: debug info on bad get_mds()

Squash me!

Signed-off-by: John Spray <john.spray@redhat.com>
include/Context: fix C_Contexts for custom context

It must not call Complete() for its immediate parent
class.

Signed-off-by: John Spray <john.spray@redhat.com>