Script options fix

This pull request fixes the following issues :
* when passing custom arguments to a script, if those arguments are
 not declared within perf, they prevent the execution of perf.
e.g.

perf script -i path/to/perf.data -s my_script -arg1 arg_value

perf will issue an error message and no processing will occur


* when passing custom arguments to a script, if those arguments are
 declared by perf, they are consumed and not passed to the script.
e.g.
perf script -i path/to/perf.data -s my_script -h

perf will display its own help message, instead of the expected help
message from my_script.

These issues are addressed as follows :
* The parse option flag is changed from PARSE_OPT_STOP_AT_NON_OPTION to
PARSE_OPT_KEEP_UNKNOWN
* A new option type is introduce OPT_CALLBACK_FINAL_OPTION, which effectively
 prevents the parsing of all options located after the script.

Signed-off-by: Adrien Bak <adrien.bak@metascale.org>

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