Bug 1074633 - RFE: Manage storage node snapshots

Added "Take Snapshot" operation to StorageNode resource. This operation
takes several other parameters and it can either move or delete older
snapshots. Basically it allows to
 - keep N latest snapshots and move/delete older ones
 - keep snapshots not older than N days and move/delete the older ones

(cherry picked from commit 2ac701032cf7b05de8a285210de619a5f62e5191)
Signed-off-by: Jirka Kremser <jkremser@redhat.com>
Bug 1074633 - RFE: Manage storage node snapshots

StorageNodeComponentItest - output more details when assertion fails

(cherry picked from commit 2de223b66109636a8b073e70e510f35cd6b70238)
Signed-off-by: Jirka Kremser <jkremser@redhat.com>
Bug 1074633 - RFE: Manage storage node snapshots

next attempt to fix storageNode takeSnapshots itests

(cherry picked from commit 0bef943a102c2bd13f42964fa35c8dd651ca9790)
Signed-off-by: Jirka Kremser <jkremser@redhat.com>
Bug 1074633 - RFE: Manage storage node snapshots

2nd piece of impl above BZ. This patch adds server side capability to manage
snapshots for storage cluster. This basically means that we regularly run
takeSnaphost operation with several parameters - so user can decide whether
to keep all of them, keep last or move older ones to specified location.

6 new private/readonly system settings have been introduced - those settings
can be updated only via Storage admin pages.

User can enable/disable snapshots management of storage cluster and set cron
expression to run management task regulary (additional 4 settings are
basically parameters for takeSnapshot operation introduced within previous
commit for this BZ). When Cluster Setting is saved in UI we re-schedule
takeSnapshot operations on all StorageNode resources in inventory.

Snapshot related code was removed from
StorageNodeManagerBean#runClusterMaintenance()

(cherry picked from commit 6640eabc6735327f8261f0fed23afd942d0ce801)
Signed-off-by: Jirka Kremser <jkremser@redhat.com>