Test changes in descriptors

Working on legacy/trac#30733 (moved) asn pointed out that there're no tests to check the changes in descriptors.

It'll be easier to create these tests when:

• sbws can use chutney (legacy/trac#33150 (moved)) so that the test network lives longer than the 1st consensus
• RelayList can be initialized with different consensus/descriptors and not only a controller (legacy/trac#29717 (moved))
• have an external tool that check the generated bandwidth files in the Tor network and detects changes in the descriptors (legacy/trac#33152 (moved))

Maybe we should include this ticket as part of legacy/trac#33121 (moved)