bots: Ensure get_temp_dir() exists
bots: Ensure get_temp_dir() exists

This allows us to use this function in a selenium context, where it runs
in a partial copy of the cockpit bots tree in our test VM.

cockpituous/cockpit,deryni/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,deryni/cockpit,cockpituous/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,cockpit-project/cockpit,cockpituous/cockpit,deryni/cockpit,martinpitt/cockpit,cockpituous/cockpit,garrett/cockpit,deryni/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,mvollmer/cockpit,cockpituous/cockpit,garrett/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,martinpitt/cockpit