Also honour any XDG variables if set (such as Wikimedia CI does)
so that gate jobs can automatically persist the cache.
Bug: T203694
Change-Id: I156af1c5097b8a87be228345fc0a0b80bb3ae338
Previously, the help message was only shown when invoking the script
without parameters. Now, if invoking it with incorrect or mispelled
parameters, it shows what you can do instead (and no more exception trace,
which it did before).
Also document clearly but briefly how to use it, and with examples.
Change-Id: Ib5ba3dc02c54039495a33d6e0cc4d026ca708ba1
This should make it easier to test, and would also allow other repositories
to create an instance of it in a maintenance script of their own.
Change-Id: I6a28e184f80eb38b5c25a0be5a9041f0c587c852
