Use len of set to check for duplicates in list of packages.
Use len of set to check for duplicates in list of packages.

Resolves: #154.

Checking for equality of the two lists was a mistake, since
the order of the list generated from the set is undefined.

rhinstaller/blivet,rvykydal/blivet,vpodzime/blivet,AdamWill/blivet,jkonecny12/blivet,AdamWill/blivet,vojtechtrefny/blivet,rvykydal/blivet,jkonecny12/blivet,rhinstaller/blivet,vpodzime/blivet,vojtechtrefny/blivet