Make albatross-provision one binary

[reynir]

albatross-provision has subcommands ca and request that serve the same purpose as albatross-provision-ca and albatross-provision-request respectively.

The binary is about the same size as either of the previous binaries. In the (compressed) debian package this results in a further ~3MB reduction of size.

[hannesm]

hmm, this leads to quite wordy invocations "albatross-provision ca sign" -- why not flatten that, "albatross-provision sign"?

[reynir]

That's a good point. I chose this way out of laziness as it seemed to me to require touching less of the code. But I like merging the commands.

[hannesm]

I took the liberty to rebase and merge the subcommands into albatross-provision (as remarked above).