[Bug 1850754] [NEW] ceph-volume lvm list is O(n^2)

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[Impact]
ceph-volume lvm calls take too much time and the time grows exponentially.
A simple call may take several minutes depending on the LV configuration.

[Test Case]
1. Create a setup with a large number of disks and logical volumes (e.g. 24)
2. Call ceph-volume lvm list for one of the disks.
3. Wait for the call to finish.

[Regression Potential]
Patch introduces LV caching, so changing LVs while ceph-volume is running may lead to race conditions.

[Other Info]
Original bug description:
 
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 * Anticipate questions from users, SRU, +1 maintenance, security teams and the Technical Board
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ceph-volume lvm list calls take very long time due to the fact it has
been implemented with O(n^2). This leads to unproportionally long
execution time taking under consideration the fact that no complex
computation is needed.

Steps to reproduce:
1. Create a setup with a large number of disks and logical volumes (e.g. 24)
2. Call ceph-volume lvm list for one of the disks.
3. Wait for the call to finish.

Expected result:
Call is executed within seconds at most.

Actual result:
Call may take even minutes in some circumstances (large number of disks, some OSDs stopped).

** Affects: ceph
     Importance: Unknown
         Status: Unknown

** Affects: cloud-archive
     Importance: Undecided
         Status: New

** Affects: ceph (Ubuntu)
     Importance: Undecided
     Assignee: Dariusz Gadomski (dgadomski)
         Status: New

** Affects: ceph (Ubuntu Bionic)
     Importance: Undecided
         Status: New

** Affects: ceph (Ubuntu Eoan)
     Importance: Undecided
         Status: New


** Tags: patch
-- 
ceph-volume lvm list is O(n^2)
https://bugs.launchpad.net/bugs/1850754
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