sqlite: add a hidden --db-backend flag

Add a hidden flag to set the database backend and plumb it into
podman-info.  Further add a system test to make sure the flag and the
info output are working properly.

Note that the test may need to be changed once we settled on how
to test the sqlite backend in CI.

Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

libpod/define/info.go

@@ -34,6 +34,7 @@ type HostInfo struct {
 	Conmon            *ConmonInfo      `json:"conmon"`
 	CPUs              int              `json:"cpus"`
 	CPUUtilization    *CPUUsage        `json:"cpuUtilization"`
+	DatabaseBackend   string           `json:"databaseBackend"`
 	Distribution      DistributionInfo `json:"distribution"`
 	EventLogger       string           `json:"eventLogger"`
 	Hostname          string           `json:"hostname"`