Fix host user parsing on AIX

[pgimalac]

The output of w looks like that:

  11:46AM   up 10 days,   1:20,  1 user,  load average: 2.03, 2.14, 2.23
User     tty          login@       idle      JCPU      PCPU what
root     pts/0       11:48AM          0         0         0 w

For some reason the current version tries to ParseFloat the User and tty fields, which are strings, so it fails and doesn't fill them. The PR fixes this by assigning directly the value to the fields.

Note: the login@ column could be mapped to the Started field, but it would require parsing the value and knowing the date and timezone.

[shirou]

LGTM. Directly assigning the string fields makes the parsing simpler and more robust. Thanks!