Restrict characters in Boot form

[AdrianDAlessandro]

It appears like whitespace is not valid in the session name for the drunc session, but our form allows whitespace characters to be submitted. We should include a validation step to prevent that.

[cc-a]

Wouldn't put this as high priority as as I understand it the boot button is a temporary convenience we're using for development and won't be part of the deployed UI so I'm not too worried about the from logic.