Some "insecure" options are hardcoded to true

[wkloucek]

Describe the bug

Some REVA "insecure" configurations default to true.

Expected behavior

"insecure" options (most of the time it's SSL cert validation check skip) must be configurable and default to false.

Actual behavior

some "insecure" options default to true, eg.

• https://github.com/cs3org/reva/blob/a133b602f6259335f1a799434d15b712d960800d/cmd/reva/main.go#L114
• https://github.com/cs3org/reva/blob/8485d4046dbc4f8b4395d82eea78129b928833bb/cmd/reva/download.go#L108
• https://github.com/cs3org/reva/blob/a8c61401b662d8e09175416c0556da8ef3ba8ed6/pkg/cbox/utils/tokenmanagement.go#L67

GRPC connections use also the insecure option (https://grpc.io/docs/guides/auth/#go)

• https://github.com/cs3org/reva/blob/63cd96849ff22995752d393c357854dcd503d0b5/pkg/rgrpc/todo/pool/pool.go#L87-L90