Change --tls-accept-all-certs from String to switch in cb-env register

[Westwooo]

cbenv-register takes a flag tls-accept-all-certs that controls if all certs will work. Currently this is a String where it should be a switch. That is, if the flag is present then the value of the associated variable should be true, else it should be false. For an example see the save flag on the same command.