[execo_g5k] Fix check_deployed_command to account for miniOS or NVMe drives

This fixes two issues:

• while kadeploy is running, we get SSH access to the deployment miniOS. The current check_deployed_command was wrongly classifying the node as "deployed" in that case.

• Grid'5000 now has clusters with NVMe drives, and the current regexp was not handling that case (e.g. /dev/nvm0n1pX instead of /dev/sdbX). It would wrongly classify the node as "undeployed" even though it was already deployed.

This changes the logic to a positive one.

Note that I couldn't actually test this with execo. This is a kind of "backport" of the same change in Enoslib (that I tested):

discovery/enoslib!138 (merged)