Mutable publisher and filenode now track the happy parameter
Adds _servers_with_shares to ServermapUpdater

When calculating the query boundary for updates to mutable files,
instead of using servers that used to have shares, use servers we
have added to the servermap. This way the querying process won't finish
until we have finished interacting with the servers that have shares.

This fixes the race condition which sometimes caused the querying process
to finish before the updater was done talking to servers with shares.
Adds servers of happiness test to mutable peer selection
Increases the number of servers for test_system.SystemTest.test_mutable

This is needed to pass the servers of happiness test.
Lowers happiness requirements for test_system.SystemTest.test_filesystem