Add loan management CLI

Adds "bkr loan-grant" and "bkr loan-return" commands.

Also adds a private RESTful API for loan management. This
will be made public once loans exist as a separate part of
the data model, with recorded start and finish dates.

Bug: 734212
Change-Id: I150083a00dd6ea510ebe8eb0e2516aa44121e7cb
Group root passwords shared with all group members

This patch makes the root password of a group visible to all
group members.

Bug: 1020091
Change-Id: I4f8f3bf06000e29ce0e7d84600650f6a689ff288
Digest auth for beaker-log-delete.

This change also replaces the 'log-delete' command with 'beaker-log-delete'

Bug: 968847
Change-Id: I522f1132d3142da82403e9825d0d2fa1c6c1cecb
Test fix. Ensure candidate systems are not clobbered by beakerd.process_new_recipes().
bkr policy-list --mine: Check if the user is authenticated

During QA it was found that there was no check being done if the user
was authenticated when the --mine flag was supplied.

Bug: 1014899
Change-Id: I14f0541dd95067e74a85d2ba8f99db4b86add9bb
Fix loan CLI usage examples

The correct option is --recipient, not --user.

Bug: 1039498
Change-Id: Ia89bc377c6f293e4e406bce68f87e6674a6b2e30
Merge branch 'release-0.15' into develop