Giving more detail in pg_upgrade errormessage

Looking at the upgrade question in [0] made me realize that we discard
potentially useful information for troubleshooting.  When we check if the
cluster is properly shut down we might as well include the status from
pg_controldata in the errormessage as per the trivial (but yet untested)
proposed diff.

Is there a reason not to be verbose here as users might copy/paste this output
when asking for help?

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Daniel Gustafsson

[0] CACoPQdbQTysF=EKckyFNGTdpOdXXMEsf_2ACno+bcNqQCB5raA@mail.gmail.com