Linux: Removing threadpool_open and threadpool_close along with SM st…

…ates (#416)

* Specs for removing threadpool open and close and SM states

* Linux Threadpool open and close removal

* Addressed Dan's and Jelani's comments

* Removed umock_c_reset_all_calls and other comments

* Replaced Sleep(1) with locking mechanism in threadpool_long_task and threadpool_long_task_v2

* Miscellaneous code space alignment issues

* Removed locks around free

* Fixing some INTEG failures

* Changed exclusive locks in threadpool_schedule_work_item to shared and limited the exclusive locks

* Changed the test locks to exclusive for threadpool_long_task_v2

* Adding Sleep(1) for threadpool_long_task_v2 and replacing exclusive locks with shared

* Another fix for the failing tests

* threadpool_long_task_v2 has exclusive lock and Sleep(1)

* Fix for the Threadpool test failures