allow override of "stdin" filename

[jsleeio]

what is this PR doing?

added a commandline option --filename to allow overriding the stdin filename displayed when accepting manifests from standard input

why is it useful/desireable?

I have a loop that kinda looks like the below (pseudo)shell example. A Helm template is rendered to a temporary file (greatly simplified here for brevity) so that the test output displays a filename for any failed tests.

The --filename option provided by this PR allows me to delete all the temporary file handling (mktemp etc) and simply pipe the output of helm template ... directly to kubetest.

#!/bin/sh
rc=0
cd $HELM_CHART
for values in envs/*yaml; do
  for template in templates/*yaml; do
    helm template . -x $template -f $values > temporary.yaml
    if ! kubetest -t $TESTS temporary.yaml ; then
      rc=1
    fi
    rm -f temporary.yaml
  done
done
exit $rc

behavioural changes

The default behaviour of kubetest is not affected by this PR.

[princerachit]

Can you retrigger the build?