Due to systemd bug, couchbase server would fail starting. We need to document this for users.

Starting couchbase server using systemctl command might fail on centos7.

When I started SPOCK using 'service couchbase-server start', as root user, it failed with this error

"Failed to start couchbase-server.service: Access denied"

I googled and found this related systemd bug

https://major.io/2015/09/18/systemd-in-fedora-22-failed-to-restart-service-access-denied/

Solution is to run

'systemctl daemon-reexec'

then run 'service couchbase-server start' again.

Since this is not couchbase-server bug but user might encounter same issue, thus we need proper document for this.