Minor maintenance to switch_branch and start_sprint

[rfay]

This PR just fixes up some annoying minor problem

• the drush si in start_sprint.sh now properly sets the site name. It was being lost before due to quoting issues.
• Minor improvements to switch_branch.sh so it doesn't stumble on the replacement of coder module (which includes its git folder and shouldn't)
• Minor env additions to tests to try to get them to fail more gracefully.

[rfay]

Thanks for taking a look!

Yes, $RANDOM is a standard shell feature from clear back in bourne shell.

The switch_branch script is tested here, if that's what you mean: https://github.com/drud/quicksprint/blob/6a6727dcea1b3d7613f213ee445c929ef8370b69/tests/installation.bats#L65-L70

[mradcliffe]

Ah, it is tested. Cool.