Post-mortem: Upgrade failure during checks phase with `no such file or directory`

Version: 5.2.x

What happened:
Gravity upgrade failed in checks phase, with an error “no such file or directory”.

Error executing function "upgrade": "
ERROR REPORT:
Original Error: *status.statusError rpc error: code = Unknown desc = no
 such file or directory
Stack Trace:
	/gopath/src/github.com/gravitational/gravity/lib/rpc/client/discovery.go:34 github.com/gravitational/gravity/lib/rpc/client.(*client).GetSystemInfo
	/gopath/src/github.com/gravitational/gravity/lib/checks/server.go:116 github.com/gravitational/gravity/lib/checks.GetServerInfo
	/gopath/src/g
ithub.com/gravitational/gravity/lib/update/validate.go:55 github.com/gravitational/gravity/lib/update.validate
	/gopath/src/github.com/gravitational/gravity/lib/updat
e/phase_checks.go:107 github.com/gravitational/gravity/lib/update.(*updatePhaseChecks).Execute
	/gopath/src/github.com/gravitational/gravity/lib/fsm/fsm.go:417 github
.com/gravitational/gravity/lib/fsm.(*FSM).executeOnePhase
	/gopath/src/github.com/gravitational/gravity/lib/fsm/fsm.go:351 github.com/gravitational/gravity/lib/fsm.(*

What we did to recover:
N/A customer preferred a patched version

Permanent Fix:
This is addressed as a software fix via PR https://github.com/gravitational/gravity/pull/779