jx login should run jx team after its completed to switch namespace

[jstrachan]

so that the user has their kubectl and jx setup to point to the dev namespace

[jstrachan]

actually it might be nice to add an optional --team foo argument to jx login so that if specified would switch to that teams namespace (so like typing jx team foo afterwards.

e.g.

jx login --team foo https://my-magic-url

then 1 command that sets up your ~/.kube/config and switches to the teams namespace in one go. Leaving off --team is fine too, which if there's N teams in that cluster, you'd get a pick list etc