filetop: Fix TypeError by not mixing bytes and str.
filetop: Fix TypeError by not mixing bytes and str.

When executing the filetop command tool, the following message was
generated:

Traceback (most recent call last):
  File "/usr/share/bcc/tools/filetop", line 190, in <module>
    name = name[:-3] + "..."
TypeError: can't concat bytes to str

Also, by decoding the bytes we print the strings without a leading "b'"
making the output more readable.

romain-intel/bcc,iovisor/bcc,shodoco/bcc,iovisor/bcc,mcaleavya/bcc,mcaleavya/bcc,tuxology/bcc,romain-intel/bcc,brendangregg/bcc,romain-intel/bcc,iovisor/bcc,tuxology/bcc,iovisor/bcc,tuxology/bcc,tuxology/bcc,mcaleavya/bcc,shodoco/bcc,tuxology/bcc,brendangregg/bcc,shodoco/bcc,brendangregg/bcc,mcaleavya/bcc,shodoco/bcc,brendangregg/bcc,brendangregg/bcc,mcaleavya/bcc,romain-intel/bcc,iovisor/bcc,shodoco/bcc,romain-intel/bcc