Explore: Dont set datasource in state if navigated away
Explore: Dont set datasource in state if navigated away

Datasource selection triggers a connection test, on success
the DS is set in the Explore state. If the test takes long and user
selects a different DS, and just after that the first test succeeds,
then the first DS overwrites the state.

* when test returns check if datasource is still the requested one

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