Remove hardcoded paths

* added helper functions to return variables for system we are running on
* removed hardcoded paths and socket type
Initial skeleton of backup download handler
Prototype of backup download handler
Remove some charm code from the backup handler and use the correct error response code
Basic tests for backup endpoint
Set SHA header for backup file
Correct year in copyright header
Create and remove the temp dir needed by backup
Skeleton test for serving backup files
Fleshed out download test
Add back header assertions
Test more error conditions
Use assertError response
Merge branch 'master' into download-backup
Basic integration with real Backup function
Correct package reference
Use EnvironConfig for mongo details required by Backup
Assert that password and mongo port are used correctly. (Currently a stub test.)
Change assert styles
Switch backup to use explicit username, password and addresss