Some runPostCrab cleaning

[OlivierBondu]

It seems the specification of the crabCommand API changed (or maybe they just improved the documentation 😄) and we don't need the dirty workaround around getoutput and crab report to silence the terminal from displaying the result

Namely, from their example:

    # If you want crabCommand to be quiet:
    #from CRABClient.UserUtilities import setConsoleLogLevel
    #from CRABClient.ClientUtilities import LOGLEVEL_MUTE
    #setConsoleLogLevel(LOGLEVEL_MUTE)
    # With this function you can change the console log level at any time.

    # To retrieve the current crabCommand console log level:
    #from CRABClient.UserUtilities import getConsoleLogLevel
    #crabConsoleLogLevel = getConsoleLogLevel()

    # If you want to retrieve the CRAB loggers:
    #from CRABClient.UserUtilities import getLoggers
    #crabLoggers = getLoggers()

It would avoid the silent crashes of runPostCrab.py that hide in fact crab crashes...