Show human readable times on summary

Currently the test summary shows the total time in seconds:

============== 11 passed in 174.98 seconds ==============

I propose we show a human-readable times instead:

============== 11 passed in 2:54.98 seconds =============

[nicoddemus]

Here’s how the last 2 suggestions look like, using pytest’s own summary so we can look at a real case:

====== 2377 passed, 85 skipped, 11 xfailed, 1 warnings in 342.63 seconds ======= 

Changes to:

==== 2377 passed, 85 skipped, 11 xfailed, 1 warnings in 342.63s (00:05:42) =====

I personally like it. 👍

[arthursoprana]

I guess @tadeu 's suggestion looks good. However I think using hh:mm:ss would be more interesting, e.g.,

============ 11 passed in 174.98 s (00:02:54) =============

I am aware that tests are not supposed to take hours to run, but using the complete notation seems to eliminate any confusion.