Fix fn test failed to query logs from log database (#1401)

When `fn test` failed to retrieve logs from the function
pod, it turns to query logs from the log database. However,
the logdb type flag is not set to `fn test`, hence the logdb
type is empty (even without default value) and cause `fn logs`
returns an error due to unable to find the corresponding log
database type.

This PR adds logdb type flag to `fn test` to resolve the problem.

pkg/fission-cli/cmd/function/command.go

@@ -138,7 +138,11 @@ func Commands() *cobra.Command {
 	wrapper.SetFlags(testCmd, flag.FlagSet{
 		Required: []flag.Flag{flag.FnName},
 		Optional: []flag.Flag{flag.HtMethod, flag.FnTestHeader, flag.FnTestBody,
-			flag.FnTestQuery, flag.FnTestTimeout, flag.NamespaceFunction},
+			flag.FnTestQuery, flag.FnTestTimeout, flag.NamespaceFunction,
+			// for getting log from log database if
+			// we failed to get logs from function pod.
+			flag.FnLogDBType,
+		},
 	})
 
 	command := &cobra.Command{