Make some shell functions available to job scripts

[hjoliver]

ref: #3336 (comment)

The poll function from tests/lib/bash/test_header is particularly useful (although it could do with modifying for flexible interval and timeout).

Options:

• include some test_header functions in job.sh
  • automatically available to all jobs, but risk of unnecessary bloat?
• put functions a new file, e.g. util.sh and either
  • source automatically alongside job.sh
  • or require users to explicitly source it in their job scripts

[oliver-sanders]

include some test_header functions in job.sh

I'm quite cautious of building up infrastructure around the job script, particularly if we aspire to move away from the bash job submission script in the future.

or require users to explicitly source it in their job scripts

It's not that clunky:

[runtime]
    [[foo]]
        script = """
            . $CYLC_DIR/lib/bash/functions
            poll ...
        "