Configuration Option to set default check_instance_build_time

Summary
=======
There should be a configuration option to configure the default interval for periodic process "check_instance_build_time" is 60 seconds. It can not be configured using the configuration file.
A configuration variable for the periodic task should be provided which may depict the value for the interval. It will be helpful in the the configuration.

Motivation
========
check_instance_build_time periodic process must be configurable by providing some configuration option in the config file.

Description
=========
The default interval for periodic process "check_instance_build_time" is 60 seconds. It can not be configured using the configuration file.
A configuration variable for the periodic task should be provided which may depict the value for the interval.

The default interval for this periodic process is 60 seconds. It can not be changed using the configuration file.

There is a configuration variable present 'instance_build_timeout', which denotes amount of time in seconds an instance can be in BUILD, before going into ERROR status. This same variable can be used to disable this periodic task by setting its value to 0. But there is no way to change the default timeout of periodic task. So options are only either disable it or run it per 60 seconds.

When the value of the variable 'instance_build_timeout' is set to 0, the periodic task still runs to check the value of the variable and if it is found to be 0, it returns. Instead a configuration variable for the periodic task may be provided which may denote the value for the interval as well as the disabling option(any negative value or zero).

UX
===
- No change is needed for User Interface, User Interface will remain same. Only the configuration options are updated.

Testing
======
Proper Tests would be added to check the system's behavior after adding this feature.

Outside Dependencies
==================
None

Requirements Update Required
========================
No specific Update is required for this change, if some external module is planned to be used for this functionality, then we only we will have to update the requirements list.

Doc Impact
=========
Documentation needs to be updated in order to inform the user about the changes that will be introduced. UI will remain unchanged as there will not be any changes to the User Interface, Only the configuration parameter is added. Hence, the details of the configuration parameter should be added in the OpenStack documentation.