Print more timings in sub_test

sub_test currently prints the total time it took to execute which is really
useful information at times. sub_test can run over a whole directory and
sometimes you want finer grained timing so this adds timing stats on a per
test basis.

It prints:
 - the compilation time for each compile of the test
 - the execution time for each run of the test
 - the total time for all compilations, and executions of the test

I wanted to add execution time to look at total execution time for multi-locale
perf runs, but Thomas thought (and I agree) that timing compilation and total
test time is useful as well.
Merge pull request #902 from ronawho/print-exec-time

Print more timings in sub_test

[reviewed by @thomasvandoren]

sub_test currently prints the total time it took to execute which is really
useful information at times. sub_test can run over a whole directory and
sometimes you want finer grained timing so this adds timing stats on a per
test basis.

It prints:
 - the compilation time for each compile of the test
 - the execution time for each run of the test
 - the total time for all compilations, and executions of the test

I wanted to add execution time to look at total execution time for multi-locale
perf runs, but Thomas thought (and I agree) that timing compilation and total
test time is useful as well.