Issues related to creating platform-sc deployment

[jessebrennan]

• Change storage backend bucket name environment variable to something that isn't Terraform specific (Change storage backend bucket environment variable name  #1527)
• Eradicate all HCA specifics from the top-level environment file (Eradicate singlecell.gi.ucsc.edu from the top-level environment file #1528)
• Remove deployment dirs other than dev on the non-HCA develop branch (7eb5901)
• Mention backend bucket in README's deployment instructions (Mention backend bucket in deployment README #1530)
• Fix boto credential caching so that a MFA code isn't needed for every boto command. More details on this issue and the workaround are boto3 not caching STS MFA sessions  boto/boto3#1179 (Customize boto3/botocore client instances to use the AWS CLI credential cache #1534)
• AWS region should be specified in environment, not environment.local (8f69f0c)
• Remove deployment dirs for non-dev deployments on non-hca branches (dupe, see above)

[hannes-ucsc]

All items have either been fixed or tickets have been created.