Fix bug "kstat binding does not return strings properly"

Fix https://github.com/Nexenta/nef/issues/222

Test:
#  Original output:

~# node  node_modules/kstat/examples/kstat2.js

 [{"class":"device_error","module":"sderr","name":"sd1,err","instance":1,"snaptime":184620382931730,"crtime":362002054477,"data":{"Soft Errors":0,"Hard Errors":0,"Transport Errors":0,"Vendor":86,"Product":86,"Revision":49,"Serial No":54,"Size":32212254720,"Media Error":0,"Device Not Ready":0,"No Device":0,"Recoverable":0,"Illegal Request":0,"Predictive Failure Analysis":0}}]

# Fixed output:

~# node  node_modules/kstat/examples/kstat2.js
 
[{"class":"device_error","module":"sderr","name":"sd1,err","instance":1,"snaptime":184520116487865,"crtime":362002054477,"data":{"Soft Errors":0,"Hard Errors":0,"Transport Errors":0,"Vendor":"VMware, ","Product":"VMware Virtual ","Revision":"1.0 ","Serial No":"6000c29e5c3aac2","Size":32212254720,"Media Error":0,"Device Not Ready":0,"No Device":0,"Recoverable":0,"Illegal Request":0,"Predictive Failure Analysis":0}}]


# Kstat output

~# kstat -n sd1,err
module: sderr                           instance: 1     
name:   sd1,err                         class:    device_error
        crtime                          362.002054477
        Device Not Ready                0
        Hard Errors                     0
        Illegal Request                 0
        Media Error                     0
        No Device                       0
        Predictive Failure Analysis     0
        Product                         VMware Virtual SRevision
        Recoverable                     0
        Revision                        1.0 
        Serial No                       6000c29e5c3aac2
        Size                            32212254720
        snaptime                        184775.028420504
        Soft Errors                     0
        Transport Errors                0
        Vendor                          VMware,