Shorten timeout duration for environment close

[harperj]

Proposed change(s)

The timeout duration for closing an environment was set to the
same duration as the timeout when waiting for a response from the
still-running environment. This led to long waits for the error
response when communication version wasn't matching.

This change updates the timeout duration so that we wait a fixed
timeout of 5 seconds before force-killing the environment worker.

Useful links (Github issues, JIRA tickets, ML-Agents forum threads etc.)

Types of change(s)

• Bug fix
• New feature
• Code refactor
• Breaking change
• Documentation update
• Other (please describe)

Checklist

• Added tests that prove my fix is effective or that my feature works
• Updated the changelog (if applicable)
• Updated the documentation (if applicable)
• Updated the migration guide (if applicable)

Other comments

[chriselion]

This looks good as it is, but just wanted to give one other possible approach:

• make _close() take a timeout parameter. This can default to None and use self.timeout_wait if the actual value is None
• pass 0 timeout in the cases we want to close immediately (or make _close_now() which calls _close() with 0 timeout). I think this should happen everywhere except for close() (so mismatched API, connection timeout, and invalid launch_string all close immediately)
• Keep close() using self.timeout_wait

[harperj]

I like that solution @chriselion. I've made the change.