Use retry func while trying to ping SQL datastore (#630)

* Use retry func while trying to ping SQL datastore

 - implements retry func specifically for SQL datastore ping
 - fmt fixes
 - using sqlx.Db.PingContext instead of sqlx.Db.Ping
 - propogate context to SQL datastore

* Rely on context from ServerOpt

* Consolidate log instances

* Cleanup

* Fix server usage in API tests

api/logs/log_test.go

@@ -5,6 +5,7 @@ import (
 	"os"
 	"testing"
 
+	"context"
 	"github.com/fnproject/fn/api/datastore/sql"
 	logTesting "github.com/fnproject/fn/api/logs/testing"
 )
@@ -13,12 +14,13 @@ const tmpLogDb = "/tmp/func_test_log.db"
 
 func TestDatastore(t *testing.T) {
 	os.Remove(tmpLogDb)
+	ctx := context.Background()
 	uLog, err := url.Parse("sqlite3://" + tmpLogDb)
 	if err != nil {
 		t.Fatalf("failed to parse url: %v", err)
 	}
 
-	ds, err := sql.New(uLog)
+	ds, err := sql.New(ctx, uLog)
 	if err != nil {
 		t.Fatalf("failed to create sqlite3 datastore: %v", err)
 	}