Make sure that each scenario gets a separate temp-dir

[josteinaj]

This was originally the intention, but I never got around to fixing it as it wasn't critical. Is there a use-case for not using separate temp-dirs?

Currently we need to repeat the directory paths in each scenario, which is kind of annoying:

<x:scenario label="_">
    
    <x:call step="my:script">
        <x:option name="some-option" select="..."/>
    </x:call>
    
    <x:scenario label="scenario 1">
        <x:call>
            <x:option name="result-dir" select="resolve-uri('1/result-dir',$temp-dir)"/>
            <x:option name="some-other-option" select="..."/>
        </x:call>
        <x:context>...</x:context>
        <x:expect>...</x:expect>
    </x:scenario>
    
    <x:scenario label="scenario 2">
        <x:call>
            <x:option name="result-dir" select="resolve-uri('2/result-dir',$temp-dir)"/>
        </x:call>
        <x:context>...</x:context>
        <x:expect>...</x:expect>
    </x:scenario>
    
</x:scenario>

Ideally we should be able to just set this at the top-level scenario, and then each sub-scenario can inherit this and still get separate temp-dirs:

<x:scenario label="_">
    
    <x:call step="my:script">
        <x:option name="result-dir" select="resolve-uri('result-dir',$temp-dir)"/>
        <x:option name="some-option" select="..."/>
    </x:call>

    <x:scenario label="scenario 1">
        <x:call>
            <x:option name="some-other-option" select="..."/>
        </x:call>
        <x:context>...</x:context>
        <x:expect>...</x:expect>
    </x:scenario>

    <x:scenario label="scenario 2">
        <x:context>...</x:context>
        <x:expect>...</x:expect>
    </x:scenario>

</x:scenario>