Fix for init script for other procs with "telegraf"

The init script fails if another process has the word "telegraf" in
it, for example if you aren running "vi /etc/opt/telegraf/telegraf.conf"
or "tail -f /var/log/telegraf/telegraf.log".  This is because
the "-f" flag to "pgrep" will show processes with the search
string anywhere in the command-line.

This patch turns it around and gets the "ps" output for the process
in the pidfile, and if that line has "telegraf" in it, it considers
it to be running.

Closes #266
Closes #267