Shell script runners don't correctly serialize "False" value for boolean parameters

I found out this issue while working on the release.

Currently, the script runner doesn't include "False" values for boolean parameter (https://github.com/StackStorm/st2/blob/master/st2common/st2common/models/system/action.py#L277) which means it won't work correctly in scenarios where boolean script parameter is not the last parameter.

For example, from one of our actions:

Script file:

Action metadata file:

---
name: st2_chg_ver_for_st2
description: Change the version for the st2 repo
enabled: true
runner_type: remote-shell-script
entry_point: st2_chg_ver_for_st2.sh
parameters:
    project:
        type: string
        description: Project name for st2
        default: st2
        position: 0
    version:
        type: string
        description: Version to update to. Should include the patch e.g. 0.1.0
        required: true
        position: 1
    fork:
        type: string
        description: Fork to use
        default: StackStorm
        position: 2
    branch:
        type: string
        description: Branch to update
        default: master
        position: 3
    update_mistral:
        type: boolean
        description: If true, update mistralclient version in requirements.txt.
        default: false
        position: 4
    update_changelog:
        type: boolean
        description: If true, update version in changelog.
        default: false
        position: 5
    local_repo:
        type: string
        description: Location where to clone the repo. Programmatically determined if not provided.
        position: 6
    dir:
        immutable: true
        default: /home/stanley/
    sudo:
        immutable: true
        default: false
    cmd:
        immutable: true
        default: ""
    kwarg_op:
        immutable: true
        default: "--"

...
#!/bin/bash
set -e

PROJECT=$1
VERSION=$2
FORK=$3
BRANCH=$4
UPDATE_MISTRAL=$5
UPDATE_CHANGELOG=$6
LOCAL_REPO=$7
GIT_REPO="git@github.com:${FORK}/${PROJECT}.git"
CWD=`pwd`
PUSH=0
....

In this case, if update_mistral and update_changelog parameters default to False, script will get incorrectly called with the following arguments st2_chg_ver_for_st2.sh st2 3.1dev StackStorm master st2_1556296602_602 which is incorrect since argument number 4 will now be local_repo instead of update_mistral.

Actual command line should look like this: st2_chg_ver_for_st2.sh st2 3.1dev StackStorm master 0 0 st2_1556296602_602. In short, False should get serialized as 0 (and we need to document this).