and '(remote,) = ctx.cluster.only(role).remotes.iterkeys()' would fail with
ValueError and no message if there were less than 0 or more than 1 key.
Now a new function, get_single_remote_value() is called which prints out
more understandable messages.
Fixes: 7510
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>
Signed-off-by: Warren Usui <warren.usui@inktank.com>
This buys us, also, the ability to select remotes by rule, i.e.
"any osd or mon gets calamari-agent installed"
Signed-off-by: Dan Mick <dan.mick@inktank.com>
