Run some filesystem integration tests

Previously no integration tests ran, now we see:

Tests run: 43, Failures: 0, Errors: 0, Skipped: 8
Enable some Xlint warnings

Also address a handful of warnings.
Reduce testFileGetParallel input size to ~160 KB

Previously this test downloaded 45 MB in 30 seconds which failed on
slower connections, causing spurious test failures.  The larger input
size provides no benefit.
Upgrade to Guava 15.0-rc1

Release notes:

https://code.google.com/p/guava-libraries/wiki/Release15
[trivial] Simplify use of Optional.or

Also correct checkArgument call.
Explain expected result in filesystem test
Upgrade to Guava 15.0

Release notes:

https://code.google.com/p/guava-libraries/wiki/Release15
Revert "Disable timed temporary signed URLs for AWS-S3"

This reverts commit bc0abbaa073a9178f3aeb0d1541ea5fc50dded35 and
re-enables temp-signed URLs for S3.

Closes JCLOUDS-200
Delete containers after integration tests

Also return newly allocated containers to the pool.
[trivial] Remove unused variables
[JCLOUDS-279] Remove spurious executable bit
Add test for correct and incorrect contentMD5

Tested against atmos (skipped), aws-s3, azureblob, cloudfiles-us, and
filesystem (skipped).
Add Atmos-specific MD5 checksum header

Tested against Atmos Online.
JCLOUDS-277: Made the description in org.jclouds.compute.domain.Image nullable
Skip unimplemented test with transient blobstore
JCLOUDS-269: Report ram as MB rather than GB for SoftLayer
JCLOUDS-282: Add NL to assignable locations for SoftLayer

- zone contained NL, so needed to add it to SoftLayerProviderMetadata's
  iso3166Codes
JCLOUDS-267. Add SecurityGroupExtension support for Nova.
JCLOUDS-286: Add a statement to install Chef using Omnibus
Remove BlobStore Map abstractions

These provide little end-user benefit and make evolving the core API
more difficult.  We deprecated these in 1.6.0.