Allow to disable Slurm's spank plugin to manage tmpfs mounts

[mboisson]

This fixes #336

[cmd-ntrf]

$enable_tmpfs_mounts is used in profile::slurm::base but defined in profile::slurm::node.

Move $enable_tmpfs_mounts in profile::slurm::base and add a lookup for it in profile::slurm::node. The new parameter will also need to be documented in the README.md.

[mboisson]

Fixed.

[mboisson]

Hum, the PR now fails if

profile::slurm::base::enable_tmpfs_mounts 

is not defined in the hieradata, with

Mar 13 19:22:37 nodegpupool1.int.hackqc-b.calculquebec.cloud puppet-agent[2555]: Could not retrieve catalog from remote server: Error 500 on SERVER: Server Error: Function lookup() did not find a value for the name 'profile::slurm::base::enable_tmpfs_mounts' on node nodegpupool1