Fix array expansion with bash 3.x

[mbaldessari]

On macosx which has bash 3.x

    michele@Micheles-Mac-mini ~ % bash --version
    GNU bash, version 3.2.57(1)-release (arm64-apple-darwin25)

    michele@Micheles-Mac-mini ~ % cat /tmp/t.sh
    set -euo pipefail

    PKI_HOST_MOUNT_ARGS=()
    echo "FOO"
    echo "${PKI_HOST_MOUNT_ARGS[@]}"
    michele@Micheles-Mac-mini ~ % /tmp/t.sh
    FOO
    /tmp/t.sh: line 6: PKI_HOST_MOUNT_ARGS[@]: unbound variable

Where as the same just works on bash 4.x/5.x:

    bash --version
    GNU bash, version 5.3.9(1)-release (x86_64-redhat-linux-gnu)
    ❯ cat /tmp/t.sh
    set -euo pipefail

    PKI_HOST_MOUNT_ARGS=()
    echo "FOO"
    echo "${PKI_HOST_MOUNT_ARGS[@]}"
    ❯ /tmp/t.sh
    FOO
    ❯

We fix this by using the expression:

${VAR_ARRAY[@]+"${VAR_ARRAY[@]}"}

This works both on bash 3.x and also the newer ones. Tested on linux
with bash 5.x and on Mac OSX with bash 3.x

[mbaldessari]

Once I soak this for a bit here in MCG I'll push to patternizer

[dminnear-rh]

LGTM