tests: Add launcher for zdtm tests

The plan is to run several tests in a "container",
ten migrate it locally, then check that all is OK.

The added set of scripts implement the first part --
they create this small container and run tests in it.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
test: Add migration in between

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
test: Don't open /dev/null before remounting ns

The file will get treated as alien. Need to fix somehow :\

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
phaul: Add option for writing pidfile of restore task

This is pretty temporary :( PID makes little sense w/o
the htype, but for tests we need one.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
test: Kill proper pid after migration

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>