The `ExecStart=` option of systemd must take arguments fully quoted.
That is,
"-sshargs=-i somekey"
and not
-ssargs="-i somekey"
Additionally, inside arguments passed to unison, `=` characters must
be quoted. After unquotation by systemd, one must have
-sshargs=-o Foo\=4
instead of
-sshargs=-o Foo=4