add arm64-efi system pool subvol exclusion. Fixes #2186

[phillxnet]

Add boot/grub2/arm64-efi subvol exclusion to our existing system pool subvol exclusions. As an appliance we attempt to hide the less commonly applicable shares as they relate only to the system directly.

Fixes #2186

Summary:

• Builds on "add root subvol exclusion mechanism. Fixes add root subvol exclusion mechanism #1931" pr.
• Includes both non boot to snap, and boot to snap patterns.

Please see issue text for a little more info:

Testing:

Prior to pr we have:

Post pr we have:

And the consequent debug log entries also indicate a purposeful exclusion post pr:

[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(@).                                                                
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(.snapshots).                                                       
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(opt).                                                              
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(root).                                                             
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(srv).                                                              
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(tmp).                                                              
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(var).                                                              
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(usr/local).                                                        
[24/Jun/2020 16:14:32] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(boot/grub2/arm64-efi).                                             
[24/Jun/2020 16:14:33] DEBUG [fs.btrfs:779] Skipping excluded subvol: name=(.snapshots/18/snapshot).                                           
[24/Jun/2020 16:14:34] DEBUG [storageadmin.views.share_helpers:111] ---- Share name = home.                                                    
[24/Jun/2020 16:14:34] DEBUG [storageadmin.views.share_helpers:113] Updating pre-existing same pool db share entry. 

Note that debug logging was enable via:

/opt/rockstor/bin/debug-mode ON

[phillxnet]

@FroggyFlox I'm included to pop this one in without formal review as it's essentially proven and trivial; and involves no additional mechanism. We can then include it in our next release so we don't surface this sensitive subvol unnecessarily on efi aarch64 builds.

[FroggyFlox]

@phillxnet, I agree.

Thanks for taking care of this!

[phillxnet]

@FroggyFlox Cheers. I'll get this merged so I can set to on the remaining architecture awareness issue.