leaper.py: indicate if origin differs from the expected origin.

[jberry-suse]

Minor and perhaps others have a better idea for wording, but I find myself squinting to see if the origin has changed when reading the comment.

Example output:

INFO:leaper.py:checking 448728
INFO:leaper.py:SUSE:SLE-12-SP2:Update/libzypp.3458@6256a456cdd115084ec37121e16af717 -> openSUSE:Leap:42.3/libzypp
INFO:leaper.py:expected origin is 'SUSE:SLE-12-SP2:Update' (unchanged)

Could make it more like a sentence: origin matches the expected origin '...' and origin (does not match|differs from) the expected origin '...'.

[coveralls]

Coverage remained the same at 46.816% when pulling 6275fc5 on jberry-suse:origin-changed into d21dbfb on openSUSE:master.

[jberry-suse]

Using startswith(), this will indicate origin openSUSE:Leap:42.2 is unchanged from openSUSE:Leap:42.2:Update which seems consistent with the logic and handling. Alternatively, this could be replaced with equals check.