Consider supporting older versions of LAFS

[nejucomo]

Currently we only support Tahoe-LAFS versions 1.10 and later (as seen in #1). However, there may be large user bases relying on older versions, perhaps if they are using official debian or ubuntu packages.

Ticket goals:

• Figure out which versions ubuntu and debian long-term support releases use.
• Ask existing lafs-giab users which versions they use and what distribution mechanism they use.
• Decide whether or not to add support for these.