Add privilege aware execution handler

[aarontp]

Currently Turbinia assumes that it runs as a user with sudo privileges. We should add methods to the TurbiniaTask object to handle executing privileged commands rather than hard-coding sudo into commands being run.

[beamcodeup]

Additional suggestion: We can harden sudo by properly restricting who can use sudo and what can be used with sudo in the sudoers config file.

[rgayon]

In the mean time, should we add "sudo" to all command execution that might need to be run with elevated privileges?

Use case is image_export.py parsing a disk.image file with chmod 000 in a GoogleCloudDiskRawEmbedded

[jleaniz]

@aarontp is this solved now that we run insider docker containers and workers are privileged/we can define the user to run as within the Dockerfile?

[aarontp]

Yeah, we can probably close this one out now.