In python3, the find method requires a bytes-like object. It fixes the
following error:

$ dbslower mysql -x $(which mysqld)
Traceback (most recent call last):
  File "/usr/share/bcc/tools/dbslower", line 72, in <module>
    if mysql_func_name.find("COM_DATA") >= 0:
TypeError: a bytes-like object is required, not 'str'

Also the -x option is currently undocumented in the man page and the
example file. So let's ix that too.

This tool traces MySQL/PostgreSQL queries, including an optional
minimum duration threshold. This is based on `mysqld_qslower` but
adapted to automatically detect MySQL/PostgreSQL processes, and a
couple of other code fixes.

I believe at this time, `mysqld_qslower` can be retired, as this
tool completely supersedes it.