Don't link manila for /home to manila for /project in caas

[sjpb]

Enables making the use of manila for /home in CaaS clusters an explicit opt-in via azimuth-ops configuration. This is to avoid the current situation where:

1. Deploy vanilla Azimuth
2. Deploy a Slurm cluster, gets Cinder home
3. Enable the project share support in Azimuth
4. Patch the Slurm cluster - existing data in /home gets deleted

[mkjpryor]

LGTM

[sjpb]

Testing at this commit:

• Created azimuth without setting azimuth_openstack_manila_project_share_gb
• Created slurm had no /project and /home was cinder - correct
• Reprovisioned azimuth with azimuth_openstack_manila_project_share_gb: 10
• New slurm had /project but /home was still cinder - correct

[mkjpryor]

I have also verified that the following works:

1. Created azimuth without setting azimuth_openstack_manila_project_share_gb
2. Created slurm had no /project and /home was cinder - correct
3. Reprovisioned azimuth with azimuth_openstack_manila_project_share_gb: 10
4. Update of existing slurm picks up /project but /home was still cinder - correct