Port ReloadConfiguration() API from snappy branch

[Barry Warsaw]

The snappy branch of si has a ReloadConfiguration() D-Bus method which takes a file system path containing the new configuration to load. This is used in the A/B partition checks.

This needs to be ported to si 3.0, but remember that the configuration path is now a directory. Also remember that the cached UpdateAvailableStatus must be invalidated so that any check after a reload does a full check.

This is somewhat dependent on LP: #1413265 since the rejiggering of the checking lock required by the proper addition of reload, triggers that bug in udm.

[James Hunt (jamesodhunt)]

See also bug 1415921.

[Barry Warsaw (barry)]

Or, maybe we don't need or want the ReloadConfiguration API after all. See for further discussion: https://code.launchpad.net/~jamesodhunt/snappy/fix-reload-configuration-logic/+merge/247829/comments/613609

[Barry Warsaw (barry)]

After further discussion, we will not be porting ReloadConfiguration to the 3.0 branch.