F #260: Allow not mounting Swap automatically

[Th0masL]

Changes proposed in this pull request:

• Allow user to provide a Context Variable called DISABLE_SWAP with the value true to prevent the one-context.d scripts to automatically try to mount the Swap file

[Th0masL]

To address https://github.com/OpenNebula/addon-context-linux/issues/260

[ospalax]

Closed in favor of this PR: https://github.com/OpenNebula/addon-context-linux/pull/262