Add --signed-url option to blob read and write

This will allow future automation to script jclouds-cli and visualize
conformance of various optional features and semantic quirks.
JCLOUDS-225: Setting 'clean install' as default release preparation goals

Partially reverts 8cc82b0. Thanks to @iocanel for hunting that down!
Upgrade jclouds-karaf to Guava 15.0-rc1
Upgrade to Guava 15.0

Release notes:

https://code.google.com/p/guava-libraries/wiki/Release15
JCLOUDS-301: work around OOM with blobstore list