backport reboot tool to 1.21
Merge pull request #1098 from gabriel-samfira/1.21

backport reboot tool to 1.21

As discussed with @fwereade, this is just a backport of:

https://github.com/juju/juju/pull/1086

to the 1.21 branch.
Merge pull request #1132 from wallyworld/lp-1392514

Ensure metadata file gets closed

Fixes: https://bugs.launchpad.net/juju-core/+bug/1392514
Merge pull request #1133 from wallyworld/lp-1392514-1.21

Merge pull request #1132 from wallyworld/lp-1392514

Ensure metadata file gets closed

Fixes: https://bugs.launchpad.net/juju-core/+bug/1392514
worker/uniter/context/jujuc: symlink tools to correct destination

Hook tools were being symlinked to the unit-specific tools symlink
when the first unit was deployed. This causes problems when that
unit is destroyed, and another unit of the same service remains;
the symlinks remain broken.

We change EnsureSymlinks to dereference the target destination if
it is a symlink.

Fixes https://bugs.launchpad.net/juju-core/+bug/1391645
Merge pull request #1136 from axw/lp1391645-uniter-tools-symlinks-1.21

worker/uniter/context/jujuc: symlink tools to correct destination

Hook tools were being symlinked to the unit-specific tools symlink
when the first unit was deployed. This causes problems when that
unit is destroyed, and another unit of the same service remains;
the symlinks remain broken.

We change EnsureSymlinks to dereference the target destination if
it is a symlink.

(backport to 1.21)

Fixes https://bugs.launchpad.net/juju-core/+bug/1391645
provider/maas: stop retrying AZs when one succeeds

Derp. Forgot to break out of loop on success.

Fixes https://bugs.launchpad.net/juju-core/+bug/1392411
Merge pull request #1138 from axw/lp1392411-maas-azretry-break-1.21

provider/maas: stop retrying AZs when one succeeds

Derp. Forgot to break out of loop on success.

(backport)

Fixes https://bugs.launchpad.net/juju-core/+bug/1392411
Increment juju to 1.21-beta3
Limit collect-metrics hook to fire only on charms that have metrics declared.
Merge pull request #1144 from tasdomas/filter-collect-metrics-hook-1.21

Limit collect-metrics hook to fire only on charms that have metrics declared.
Merge pull request #1145 from sinzui/inc-1.21-beta3

Increment juju to 1.21-beta3

Update juju and the win installer to beta3.