Make test scripts run without /bin/bash

The test scripts hardcoded #!/bin/bash while they are not really
requiring bash. Use the more portable #!/usr/bin/env sh instead, so that
they use the default shell.

Signed-off-by: Tom Wieczorek <twieczorek@mirantis.com>

cmd/helm/testdata/helmhome/helm/plugins/args/args.sh

@@ -1,2 +1,2 @@
-#!/bin/bash
-echo $*
+#!/usr/bin/env sh
+echo "$@"

cmd/helm/testdata/helmhome/helm/plugins/exitwith/exitwith.sh

@@ -1,2 +1,2 @@
-#!/bin/bash
-exit $*
+#!/usr/bin/env sh
+exit "$1"

pkg/getter/testdata/plugins/testgetter/get.sh

@@ -1,8 +1,8 @@
-#!/bin/bash
+#!/usr/bin/env sh
 
 echo ENVIRONMENT
 env
 
 echo ""
 echo ARGUMENTS
-echo $@
+echo "$@"

pkg/getter/testdata/plugins/testgetter2/get.sh

@@ -1,8 +1,8 @@
-#!/bin/bash
+#!/usr/bin/env sh
 
 echo ENVIRONMENT
 env
 
 echo ""
 echo ARGUMENTS
-echo $@
+echo "$@"

pkg/plugin/testdata/plugdir/good/hello/hello.sh

@@ -1,9 +1,9 @@
-#!/bin/bash
+#!/usr/bin/env sh
 
 echo "Hello from a Helm plugin"
 
 echo "PARAMS"
-echo $*
+echo "$@"
 
 $HELM_BIN ls --all