consistently include report overview

[jeremyandrews]

• consistently report users simulated, target host(s), start and end times, and total duration of test both in text metrics and html report

For example, in the text report the following shows up at the very end:

 ------------------------------------------------------------------------------
 Users: 2
 Target host: http://apache/
 During: 2021-08-12 10:43:18 - 2021-08-12 10:43:20 (duration: 00:00:02)

 goose v0.13.1-dev
 ------------------------------------------------------------------------------

And if targeting more than one host:

 ------------------------------------------------------------------------------
 Users: 2
 Target hosts: 
 - http://10.10.3.23/
 - http://apache/
 During: 2021-08-12 10:44:19 - 2021-08-12 10:44:21 (duration: 00:00:02)

 goose v0.13.1-dev
 ------------------------------------------------------------------------------