test/py: Add a report show test durations

Execution time varies widely with the existing tests. Provides a way to
produce a summary of the time taken for each test, along with a
histogram.

This is enabled with the --timing flag.

Enable it for sandbox in CI.

Example:

   Duration : Number of tests
   ======== : ========================================
       <1ms :  1
       <8ms :  1
      <20ms : # 20
      <30ms : ######## 127
      <50ms : ######################################## 582
      <75ms : ####### 102
     <100ms : ## 39
     <200ms : ##### 86
     <300ms : # 29
     <500ms : ## 42
     <750ms : # 16
      <1.0s : # 15
      <2.0s : # 23
      <3.0s :  13
      <5.0s :  9
      <7.5s :  1
     <10.0s :  6
     <20.0s :  12

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
4 files changed