Reject 0.2.9 and 0.4.0 in dirserv_rejects_tor_version()

We should modify dirserv_rejects_tor_version() to keep it up to date with our supported versions:

After 1 January 2020, we should reject all versions less than 0.3.5.
After 2 February 2020, we should reject the 0.4.0 series, but allow the 0.3.5 series https://trac.torproject.org/projects/tor/wiki/org/teams/NetworkTeam/CoreTorReleases#Current

After these dates, we should get arma to test this change, then merge it.

After we merge, we should create a ticket in 0.4.4 to reject 0.4.1.

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