s3: Rename server_event_context() to global_event_context()

s3: Rename server_event_context() to global_event_context()

This reflects that the event context is also used outside of the server
processes.

The command used for the rename:
find . -name '*.[hc]' -print0 | xargs -0 sed -i 's/server_event_context/global_event_context/'

Signed-off-by: Christof Schmitt <cs@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>