close file before renaming

Renaming an open file is not possible on windows
Adds the 'maas-bridge-interface' option to MAAS configuration
	- By default 'eth0' is used, but this fails on some setups like LP: #1271144 when
	using (p1p2, eth2, ..) interfaces.
- Minor fixes according to @wallyworld observations
- Fixed according to @axw comment.
	- For backward-compatibility, network-bridge is an empty string by default "eth0" will be returned.
resolve one TODO, replace with two more :/
testing: AgentConfigForTag now takes a Tag not a string
state/apiserver: Return filename from Backup API

This change adds a Content-Disposition header to backup API responses
which contains the server-generated backup filename. This becomes
important once backups start being stored server side (soon) but also
simplifies the client side of the backup API (no need to generate
backup filenames).
state, etc: state.Info.Tag is now a names.Tag not a string
Reopen mongo sessions between replset initiation attempts

Also, reinstate a change made by mfoord to call
CurrentStatus after attempting intiation, and
refresh session between attempts.

https://bugs.launchpad.net/juju-core/+bug/1339240
Specify a smaller mongo oplog size on local provider

Since the local provider has a single Mongo instance,
the oplog is unuseful. We reduce the size to speed up
preallocation.
Update goamz in dependencies.tsv
Merge pull request #227 from niedbalski/fix_1271144

Add 'network-bridge' option to MAAS configuration

I exposed the variable 'network-bridge'' to allow users to specify to which network interface
the bridge should be bound to.

MAAS provider uses 'eth0' as the default network interface used to build the bridge br0, on some scenarios like LP: #1271144  (p1p2, eth2, ..) this assertion is not true.
Merge pull request #270 from axw/lp1338179-local-oplog

Specify a smaller mongo oplog size on local provider

Since the local provider has a single Mongo instance,
the oplog is unuseful. We reduce the size to speed up
preallocation.

Fixes https://bugs.launchpad.net/juju-core/+bug/1338179
Extend replSetGetStatus timeout, add a test
Merge pull request #272 from axw/lp1319474-update-godeps-goamz

Update goamz in dependencies.tsv

Fixes https://bugs.launchpad.net/juju-core/+bug/1319474
Merge pull request #271 from axw/lp1339240-mongo-replset-retry

Reopen mongo sessions between replset initiation attempts

Also, reinstate a change made by mfoord to call
CurrentStatus after attempting intiation, and
refresh session between attempts.

https://bugs.launchpad.net/juju-core/+bug/1339240
Merge pull request #266 from mjs/backup-api-filename

state/apiserver: Return filename from Backup API

This change adds a Content-Disposition header to backup API responses which contains the server-generated backup filename. This becomes important once backups start being stored server side (soon) but also simplifies the client side of the backup API (no need to generate backup filenames).
Added test to ensure backup filename only uses plain characters.
Merge pull request #225 from gabriel-samfira/close-file

close file before renaming

Renaming an open file is not possible on windows
Merge pull request #273 from mjs/backup-filename-test

Added test for backup filename

It is important that the filename is 7-bit ASCII because it is returned in a header (unencoded) by the backup API call.