Don't crash when GuardDuty is in use

[acdha]

This avoids crashing on the GuardDuty sidecars which do not have the managed agents.

Closes #67

Issue #, if available:

Description of changes:

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[bassmanitram]

That doesn't QUITE do it, because then the indices of the tasks get off and you end up with misleading info later on

THIS is my block for the same issue:

# 6. Check the managed agents' status
printf "${COLOR_DEFAULT}  Container-Level Checks | \n"
printf "${COLOR_DEFAULT}    ----------\n"
printf "${COLOR_DEFAULT}      Managed Agent Status"
if [[ "${executeCommandEnabled}" = "false" ]]; then
  printf " - ${COLOR_YELLOW}SKIPPED\n"
  printf "${COLOR_DEFAULT}    ----------\n"
else
  printf "\n"
  printf "${COLOR_DEFAULT}    ----------\n"
  agentsStatus=$(echo "${describedTaskJson}" | jq -r '.tasks[0].containers[] |
  if has("managedAgents") and (.managedAgents | length) > 0 then
    .managedAgents[] .status
  else
    "ABSENT"
  end
  ')
  idx=0
  for S in $agentsStatus; do
    containerName=$(echo "${describedTaskJson}" | jq -r ".tasks[0].containers[${idx}].name")
	if [[ "$S" != ABSENT ]]; then
        status=$(echo "${describedTaskJson}" | jq -r ".tasks[0].containers[${idx}].managedAgents[0].lastStatus")
        reason=$(echo "${describedTaskJson}" | jq -r ".tasks[0].containers[${idx}].managedAgents[0].reason")
        lastStartedAt=$(echo "${describedTaskJson}" | jq -r ".tasks[0].containers[${idx}].managedAgents[0].lastStartedAt")
	else
		status="ABSENT"
	fi
    printf "         $((idx+1)). "
    case "${status}" in
      *STOPPED* ) printf "${COLOR_RED}STOPPED (Reason: ${reason})";;
      *ABSENT* ) printf "${COLOR_YELLOW}NOT PRESENT";;
      *PENDING* ) printf "${COLOR_YELLOW}PENDING";;
      * ) printf "${COLOR_GREEN}RUNNING";;
    esac
    printf "${COLOR_DEFAULT} for \"${containerName}\""
    if [[ "${status}" = "STOPPED" ]]; then
      printf " - LastStartedAt: ${lastStartedAt}"
    fi
    printf "\n"
    idx=$((idx+1))
  done
fi

# 7. Check the "initProcessEnabled" flag added in the task definition (yellow)