wcst_import - support python_cmd to run python command in hooks

[Bang Pham Huu]

For example, one can specify the python_cmd besides the cmd in the hook, like below:

Here, "cmd" will be executed before "python_cmd".

"hooks": [
    {
      "description": "remove files with invalid bbox",
      "when": "before_import",
      "cmd": "rc=$(echo \"${gdal:minX} >= -180.0 && ${gdal:maxX} <= 180.0 && ${gdal:minY} >= -90.0 && ${gdal:maxY} <= 90.0\" | bc -l); [ \"$rc\" = 0 ] && echo \"${file:path}\" || echo valid",
      "python_cmd": "print 'Done'",
      "abort_on_error": false
    }
]

[Bang Pham Huu]

The cmd and python_cmd are exclusively. Only one of them can be used by a hook.

[Dimitar Misev]

• cmd and python_cmd should be exclusive, throw an error if both are specified
• document that the python_cmd is executed in the wcst_import python instance
• document that the disadvantage of bash cmd is that for each file a bash shell will be forked, which can be expensive for many files