Support start_period for healthcheck in Docker Compose

Signed-off-by: Li Yi <denverdino@gmail.com>

cli/compose/loader/full-example.yml

@@ -114,6 +114,7 @@ services:
       interval: 10s
       timeout: 1s
       retries: 5
+      start_period: 15s
 
     # Any valid image reference - repo, tag, id, sha
     image: redis

cli/compose/loader/loader_test.go

@@ -760,6 +760,7 @@ func TestFullExample(t *testing.T) {
 			Interval:    "10s",
 			Timeout:     "1s",
 			Retries:     uint64Ptr(5),
+			StartPeriod: "15s",
 		},
 		Hostname: "foo",
 		Image:    "redis",

cli/compose/schema/data/config_schema_v3.4.json

@@ -324,7 +324,8 @@
             {"type": "array", "items": {"type": "string"}}
           ]
         },
-        "timeout": {"type": "string"}
+        "timeout": {"type": "string"},
+        "start_period": {"type": "string"}
       }
     },
     "deployment": {

cli/compose/types/types.go

@@ -172,7 +172,7 @@ type HealthCheckConfig struct {
 	Timeout     string
 	Interval    string
 	Retries     *uint64
-	StartPeriod string
+	StartPeriod string `mapstructure:"start_period"`
 	Disable     bool
 }