Logging brooklyn-persister thread Jclouds messages in a separate file

When a server with persistence to an object store enabled manages lots of
entities the Jclouds log is overwhelmed by messages logged from the
brooklyn-persister thread (in one case logging at a rate of ~ half a
million lines every four minutes).

The appender added in this commit alleviates - a little! - this logging
overload.

Anecdotal measurements of the ratio between the persister log and jclouds
log sizes, with EmptySoftwareProcess entities:
0 entities: persister log 0.01 times size of jclouds log
1 entity: 0.36
5 entities: ~1.13
10 entities: 1.75
50 entities: 8.6
Add TestResourceUnavailableException

Provides a way to skip TestNG tests if a test resource is not available (such as in the source distribution, which does not carry binary test resources)
Make embedded jars optional

Modifies code that relies on jar files as an embedded resource to
gracefully handle cases where the files are missing. Limited to tests,
which will cause TestNG to skip the test if the resource is missing.
Required for our source distribution, as Apache convention is to not
ship binaries in releases.
Make embedded wars optional

Modifies code that relies on war files as an embedded resource to
gracefully handle cases where the files are missing. Limited to tests,
which will cause TestNG to skip the test if the resource is missing.
Required for our source distribution, as Apache convention is to not
ship binaries in releases.
Merge and close #365 [BROOKLYN-29]
Fix the DynamicMultiGroup rebind actions
BindDnsServer strips invalid characters from domain names

As per RFCs 952 and 1123.
Make BUCKETS map immutable (see review comment from @aledsage)
This closes #357
This closes #283
This closes #372

* github/pr/372:
  Make BUCKETS map immutable (see review comment from @aledsage)
  Fix the DynamicMultiGroup rebind actions