cgroups_py email argument not working due to undefined self.o_email

[syl-taylor]

In Throttler init, self.o_mail is set to o_mail (email argument's value), but in _jctl_parse(), there are 2 if statements using self.o_email, which is undefined.

(Ref: https://github.com/HPCSYSPROS/Workshop18/blob/master/cgroups_py_Using_Linux_Control_Groups_and_Systemd_to_Manage_CPU_Time_and_Memory/artifact/cgroups_py#L240)

I replaced self.o_email with self.o_mail to get the script/email notifier working, but likewise, self.o_mail in init could be changed to self.o_email.