Python 3 incompatibilities/niggles

I noticed a few scripts have issues with Python 3. E.g., funccount doesn't work:

```
$ sudo /usr/share/bcc/tools/funccount vfs_*
Traceback (most recent call last):
File "/usr/share/bcc/tools/funccount", line 93, in
addr = b.ksymname(fn)
File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 664, in ksymname
return BPF._ksym_cache.resolve_name(name)
File "/usr/lib/python3/dist-packages/bcc/__init__.py", line 79, in resolve_name
if lib.bcc_symcache_resolve_name(self.cache, name, ct.pointer(addr)) < 0:
ctypes.ArgumentError: argument 2: : wrong type
```

and biosnoop (and others) print char strings as bytes:

```
$ sudo /usr/share/bcc/tools/biosnoop
TIME(s) COMM PID DISK T SECTOR BYTES LAT(ms)
0.000000000 b'jbd2/sda1-8' 173 b'sda' W 4598320 602112 1.38
0.001985000 b'jbd2/sda1-8' 173 b'sda' W 4599496 4096 0.11
0.302378000 b'?' 0 b'' R -1 8 0.23
```

This is not an exhaustive list — we just need to go through them all and fix any issues.