fix: Add embedded kamelets directory check back

[astefanutti]

This fixes the following error message when the operator starts:

{"level":"error","ts":1613030254.0653336,"logger":"camel-k","msg":"error while listing resource files","dir":"/kamelets/","error":"open /kamelets: file does not exist","stacktrace":"github.com/go-logr/zapr.(*zapLogger).Error\n\tgithub.com/go-logr/zapr@v0.1.1/zapr.go:128\ngithub.com/apache/camel-k/pkg/util/log.Logger.Error\n\tgithub.com/apache/camel-k/pkg/util/log/log.go:75\ngithub.com/apache/camel-k/pkg/util/log.Error\n\tgithub.com/apache/camel-k/pkg/util/log/log.go:216\ngithub.com/apache/camel-k/pkg/resources.Resources\n\tgithub.com/apache/camel-k/pkg/resources/resources_support.go:105\ngithub.com/apache/camel-k/pkg/install.KameletCatalog\n\tgithub.com/apache/camel-k/pkg/install/kamelets.go:43\ngithub.com/apache/camel-k/pkg/install.OperatorStartupOptionalTools\n\tgithub.com/apache/camel-k/pkg/install/optional.go:59\ngithub.com/apache/camel-k/pkg/cmd/operator.Run\n\tgithub.com/apache/camel-k/pkg/cmd/operator/operator.go:156\ngithub.com/apache/camel-k/pkg/cmd.(*operatorCmdOptions).run\n\tgithub.com/apache/camel-k/pkg/cmd/operator.go:51\ngithub.com/spf13/cobra.(*Command).execute\n\tgithub.com/spf13/cobra@v1.0.0/command.go:846\ngithub.com/spf13/cobra.(*Command).ExecuteC\n\tgithub.com/spf13/cobra@v1.0.0/command.go:950\ngithub.com/spf13/cobra.(*Command).Execute\n\tgithub.com/spf13/cobra@v1.0.0/command.go:887\nmain.main\n\tcommand-line-arguments/main.go:48\nruntime.main\n\truntime/proc.go:204"}

Which is a side-effect of #1978.

Release Note

NONE