MINOR: stats: make "show info" able to report rates as floats when asked

MINOR: stats: make "show info" able to report rates as floats when asked

Now "show info float" will also report SSL rates, connection rates and
key reuse ratios as floats. This can be convenient at very low rates.

Note that the SSL reuse ratio which used to commonly oscillate between
0 and 1 under load is now more often above zero with small values. It
indicates that for better stability we shouldn't be comparing a key rate
with a connection rate but instead we should measure the reuse rate at
its source.