Fix tokenizing of unsupported data in vdsmapi-schema.json

vdsmapi tokenizer got into an endless loop when unsupported token was
found. Example input trigering this are invalid tokens such as unquoted
string, or valid JSON tokens like null, true and false, which are not
supported by the parser.

Now the tokenizer raise ValueError with the offending data. This should
be good enough for developers usage.

New unittests cover tokenizing valid, invalid and unspported tokens.

Change-Id: I7d29686d3189fd9e64e26c56dcd9da370f855406
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19697
Reviewed-by: Allon Mureinik <amureini@redhat.com>
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>