Add tools datasource registration framework
Remove provider storage from tools search path

Also, register OpenStack keystone search path for tools.
Revert name change
Fix azure, local, maas provider
Fix ec2 tests
Fix dummy, joyent provider tests
Fix more tests
Fix tools tests

Now we upload tools to the default tools
location (as if we controlled the public
tools container), rather than to provider
storage.
Address review comments
Remove stray line
Several fixes to avoid building jujud in tests
More fixes after rebasing
Merge pull request #804 from axw/tools-metadata-no-provider-storage

Remove provider storage from tools search path

Also, register OpenStack keystone search path for tools
and fix getKeystoneImageSource so it doesn't error if
the service isn't defined in keystone.

To minimise the impact in the short term, I've added a
"DefaultToolsStorage" field to JujuConnSuite which is
an environs.Storage that overrides the default tools
location (i.e. streams.canonical.com/juju/tools). Tests
that previously uploaded tools to provider storage now
mostly use this.