cli/command/container: some small performance optimizations for formatting stats
cli/command/container: some small performance optimizations for formatting stats

Formatting stats runs in a loop to refresh the stats for each container. This
patch makes some small performance improvments by reducing the use of Sprintf
in favor of concatenating strings, and using strconv directly where possible.

Benchmark can be run with:

    GO111MODULE=off go test -test.v -test.bench '^BenchmarkStatsFormat' -test.run '^$' ./cli/command/container/

Before/after:

    BenchmarkStatsFormatOld-8 	    2655	    428064 ns/op	   62432 B/op	    5600 allocs/op
    BenchmarkStatsFormat-8   	    3338	    335822 ns/op	   52832 B/op	    4700 allocs/op

Average of 5 runs;

    benchstat old.txt new.txt
    name           old time/op    new time/op    delta
    StatsFormat-8     432µs ± 1%     344µs ± 5%  -20.42%  (p=0.008 n=5+5)

    name           old alloc/op   new alloc/op   delta
    StatsFormat-8    62.4kB ± 0%    52.8kB ± 0%  -15.38%  (p=0.000 n=5+4)

    name           old allocs/op  new allocs/op  delta
    StatsFormat-8     5.60k ± 0%     4.70k ± 0%  -16.07%  (p=0.008 n=5+5)

Signed-off-by: Sebastiaan van Stijn <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@gone.nl>

docker/cli,cpuguy83/cli,docker/cli,cpuguy83/cli,thaJeztah/cli,thaJeztah/cli