Added dell_api_async_rest_timeout and dell_api_sync_rest_timeout to allow
setting of async and sync timeouts for the Dell EMC SC REST API.
The user should generally not set these. They should be set only when
instructed by support.
Fixed a couple of comments.
Updated documentation.
Change-Id: Id8fd27d83e2f97070f67523c9c2d8c59f66e6caa
