macOS 10.13 (APFS) may not be crash safe

Description

We do not yet have stable testing on macOS 10.13, which uses Apple's new APFS filesystem.

In particular, tests of WiredTiger's crash safety fail when run against the macOS 10.13 test system available in Evergreen.

Community users and some MongoDB engineers have been running MongoDB on macOS 10.13 for months without seeing major issues, but the test failures suggest that data may be lost if mongod is not shutdown cleanly, or if the system is powered down while mongod is busy.

Scope of changes (files that need work and how much)

Add an admonition (Warning?) that mongod processes with datafiles on an APFS (10.13+) filesystem may lose data during unclean shutdowns (e.g. power failure, or system shutdown while mongod is busy). 

Possibly point to WT-4018 for discussions and remediation. 

• Update  the Community OSX Install and Enterprise OSX Install pages
• Possibly have a more in-depth explanation under the WiredTiger FAQ
• Possibly update Production Notes Supported Platforms

May need a second linked DOCS ticket to update this admonition if a fix is released

Impact to other docs outside of this product

We might consider having a warning on the Cloud Manager and Ops Manager OSX Agent Installation pages w.r.t. 10.13+. The Troubleshooting pages may be another option.

MVP (work and date?)

At minimum, admonition on OSX installation pages. Depending on whether 4.0 includes a fix, may want to then proceed to update the FAQ and production notes.

Coordinate with cloud team on where best to update OpsManager/CloudManager docs.

Resources (e.g. Scope Docs, Invision)

See Linked Tickets