buildstats: Outputs 'task recipe elapsed-time' from each buildstats' recipe

buildstats: Outputs 'task recipe elapsed-time' from each buildstats' recipe

Given a 'buildstats' path (created by bitbake when setting
USER_CLASSES ?= "buildstats" on local.conf) and task names, outputs
'<task> <recipe> <elapsed time>' for all recipes. Elapsed times are in
seconds, and task should be given without the 'do_' prefix.

Some useful pipelines

1. Tasks with largest elapsed times

    $ buildstats.sh -b <buildstats> | sort -k3 -n -r | head
    do_compile perl-5.20.0-r1 221.82
    do_configure gettext-native-0.19.4-r0 140.34
    do_compile openssl-native-1.0.2a-r0 107.48
    do_compile openssl-1.0.2a-r0 102.10
    do_configure perl-native-5.20.0-r0 90.70
    do_configure gettext-0.19.4-r0 88.17
    do_compile gcc-cross-i586-4.9.2-r0 83.98
    do_configure m4-native-1.4.17-r0 83.44
    do_compile qemu-native-2.2.0-r1 71.69
    do_compile glibc-2.21-r0 60.88

2. Min, max, sum per task

    $ buildstats.sh | datamash -t' ' -g1 min 3 max 3 sum 3 | sort -k4 -n -r
    do_configure 0.03 140.34 1968.66
    do_compile 0.01 221.82 1664.44
    do_install 0.03 40.31 330.45
    do_populate_sysroot 0.11 34.45 229.23
    do_unpack 0.01 36.1 193.54
    do_patch 0.01 9.2 62.07
    do_fetch 0.01 6.66 32.13
    do_populate_lic 0.09 1.65 30.7

Signed-off-by: Leonardo Sandoval <leonardo.sandoval.gonzalez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>