debuginfod-find: Restore DEBUGINFOD_PROGRESS behaviour

debuginfod-find: Restore DEBUGINFOD_PROGRESS behaviour

Commit d7cb72f7 changed debuginfod-find to always set a progress
callback function in order to handle interrupts during downloading.

Previously debuginfod-find set a progressfn only when the -v command
line option was given.  If the DEBUGINFOD_PROGRESS environment variable
is set, libdebuginfod automatically sets a default progressfn as long as
no other progressfn has been set using debuginfod_set_progressfn.

Commit d7cb72f7 therefore resulted in DEBUGINFOD_PROGRESS no longer
affecting debuginfod-find when invoked without -v.

This patch restores the old behaviour: when DEBUGINFOD_PROGRESS is set
and -v is not given, the default progressfn will trigger during
downloading.

Signed-off-by: Aaron Merey <amerey@redhat.com>