Create nagios export dir if it does not exist
Merge jacekn's RT#63843 fix
[jjo, r=] completely rework leader election, and several other misc fixes
- fix relation usage: only the leader does relation-set seed-nodes,
  others "wait" (softfail if not yet present, waiting for next hook to fire)
- use cluster-relation-joined to delay non-leaders thus giving leader a
  (better) chance to make progress, relation data will appear on
  cluster-relation-changed runs
- do soft-fail if non-leader has no proper seeds yet, to allow further
  cluster-relation-changed runs (until we get the seed from the master)
- add fix_cassandra_perms after mounting perm storage
- adapt unittests

TESTS PASS via make -C tests
TESTS PASS via mojo at https://ci.admin.canonical.com/job/mojo-ue-cassandra
support unit-get private-address returning IPs, without going thru dig
[jjo, r=lazypower] completely rework leader election, and other misc fixes
- fix relation usage: only the leader does relation-set seed-nodes,
  others "wait" (softfail if not yet present, waiting for next hook to fire)
- use cluster-relation-joined to delay non-leaders thus giving leader a
  (better) chance to make progress, relation data will appear on
  cluster-relation-changed runs
- do soft-fail if non-leader has no proper seeds yet, to allow further
  cluster-relation-changed runs (until we get the seed from the master)
- add fix_cassandra_perms after mounting perm storage
- adapt unittests

TESTS PASS via make -C tests
TESTS PASS via mojo at https://ci.admin.canonical.com/job/mojo-ue-cassandra
[jjo, r=] merge from internal branch: completely rework leader election, and other misc fixes
    JuanJo Ciarlante 2014-05-19 [merge] [jjo, r=] merge from internal branch: completely rework lea...
    JuanJo Ciarlante 2014-02-26 [merge] [jjo, r=lazypower] completely rework leader election, a...
    JuanJo Ciarlante 2014-02-21 support unit-get private-address returning IPs, without going t...
    JuanJo Ciarlante 2014-02-20 [jjo, r=] completely rework leader election, and several other ...
    Nick Moffitt 2014-02-11 [merge] Merge jacekn's RT#63843 fix
    Jacek Nykis 2014-01-24 Create nagios export dir if it does not exist