[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.
SoftLayer: report ram as MB rather than GB

- fixes https://issues.apache.org/jira/browse/JCLOUDS-269