On systems without /bin/bash (e.g. NixOS), invoking tasks may fail because
of some hard-coded references to /bin/bash. Those references are either fine
(because the task runs in a container where /bin/bash *is* available),
don't matter (because the shebang is ignored) or cause failure (because
/bin/bash cannot be invoked). This commit adapts Nextflow for the last
scenario. Instead of invoking `/bin/bash`, the actually available bash
executable is called.

Signed-off-by: Rolf Schröder <[email protected]>

This is more portable. This commit also makes sure that `-ue[x]` is not
used during trace.

Signed-off-by: Rolf Schröder <[email protected]>

Signed-off-by: Rolf Schröder <[email protected]>

Signed-off-by: Rolf Schröder <[email protected]>

to use.

Signed-off-by: Rolf Schröder <[email protected]>