galera: start joining nodes during 'monitor' to allow long-running SST

Squashed commit of the following:

commit d34ea174b9abdca5101fea65d0ae594f9ec45d3c
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Mon Oct 5 12:20:45 2015 +0200

galera: document the updated boot process

commit dba7120896a53b6009aa9f91a2aa203c82444ce3
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Mon Oct 5 11:53:11 2015 +0200

galera: clean up debug and unused code

commit da4c8b6849eae9c4ae789330795a13b3a24e02ad
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Mon Oct 5 11:45:17 2015 +0200

galera: fix promotion and associated checks

commit c01d5824f601dbce4045a8259cde6c4517b24e20
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Wed Sep 23 09:58:29 2015 +0200

galera: sanity checks during promote operation

commit 04d8a36dee09ea96c7478f0205b80cdf704af18a
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Wed Sep 23 09:53:49 2015 +0200

galera: fix return code in galera_stop()

commit 22220bda1728b5ce54643650238d0a99fe997d87
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Wed Sep 23 09:42:49 2015 +0200

galera: do not promote joiner nodes in start operation

commit 60342c56ce3843f915f830104332d56833d764c6
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Mon Sep 21 12:13:28 2015 +0200

galera: prevent state change during probe

commit 1fe6415f7ec4c7b54d12696f0defc2cab2324bcf
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Mon Sep 21 12:02:44 2015 +0200

galera: improved monitoring of the syncing progress

commit fdad75f97cea2bb3a513eb61ece5f31ce2344fa8
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Fri Sep 18 01:00:20 2015 +0200

galera: code style fixes

commit 25cdde0342992fcfdef59b58083da4692ce31707
Author: Damien Ciabrini <dciabrin@redhat.com>
Date: Wed Sep 16 19:12:24 2015 +0200

galera: multi-stage cluster startup to better track long-running IST/SST