Remove Libpod special-init conditions

Before this, for some special Podman commands (system reset,
system migrate, system renumber), Podman would create a first
Libpod runtime to do initialization and flag parsing, then stop
that runtime and create an entirely new runtime to perform the
actual task. This is an artifact of the pre-Podman 2.0 days, when
there was almost no indirection between Libpod and the CLI, and
we only used one runtime because we didn't need a second runtime
for flag parsing and basic init.

This system was clunky, and apparently, very buggy. When we
migrated to SQLite, some logic was introduced where we'd select a
different database location based on whether or not Libpod's
StaticDir was manually set - which differed between the first
invocation of Libpod and the second. So we'd get a different
database for some commands (like `system reset`) and they would
not be able to see existing containers, meaning they would not
function properly.

The immediate cause is obviously the SQLite behavior, but I'm
certain there's a lot more baggage hiding behind this multiple
Libpod runtime logic, so let's just refactor it out. It doesn't
make sense, and complicates the code. Instead, make Reset,
Renumber, and Migrate methods of the libpod Runtime. For Reset
and Renumber, we can shut the runtime down afterwards to achieve
the desired effect (no valid runtime after). Then pipe all of
them through the ContainerEngine so cmd/podman can access them.

As part of this, remove the SystemEngine part of pkg/domain. This
was supposed to encompass these "special" commands, but every
command in SystemEngine is actually a ContainerEngine command.
Reset, Renumber, Migrate - they all need a full Libpod and access
to all containers. There's no point to a separate engine if it
just wraps Libpod in the exact same way as ContainerEngine. This
consolidation saves us a bit more code and complexity.

Signed-off-by: Matt Heon <mheon@redhat.com>

libpod/reset.go

@@ -90,8 +90,24 @@ func (r *Runtime) removeAllDirs() error {
 	return lastErr
 }
 
-// Reset removes all storage
-func (r *Runtime) reset(ctx context.Context) error {
+// Reset removes all Libpod files.
+// All containers, images, volumes, pods, and networks will be removed.
+// Calls Shutdown(), rendering the runtime unusable after this is run.
+func (r *Runtime) Reset(ctx context.Context) error {
+	// Acquire the alive lock and hold it.
+	// Ensures that we don't let other Podman commands run while we are
+	// removing everything.
+	aliveLock, err := r.getRuntimeAliveLock()
+	if err != nil {
+		return fmt.Errorf("retrieving alive lock: %w", err)
+	}
+	aliveLock.Lock()
+	defer aliveLock.Unlock()
+
+	if !r.valid {
+		return define.ErrRuntimeStopped
+	}
+
 	var timeout *uint
 	pods, err := r.GetAllPods()
 	if err != nil {
@@ -258,5 +274,13 @@ func (r *Runtime) reset(ctx context.Context) error {
 		prevError = err
 	}
 
+	// Shut down the runtime, it's no longer usable after mass-deletion.
+	if err := r.Shutdown(false); err != nil {
+		if prevError != nil {
+			logrus.Error(prevError)
+		}
+		prevError = err
+	}
+
 	return prevError
 }