[pve-devel] Adapt regex in pvesm import/export.

[Wolfgang Link]

We allow uppercase characters in snapshot names.
pvesm import and export must allow uppercase characters too.

[PATCH V2]
Use JSON schema instead of hardcoding.

[PATCH V3 pve-storage]
Correct typo.

[PATCH V4]
Make base snapshot more specific.

[PATCH V5]
Merge pve-lxc-snapshot-name and pve-snapshot-name in PVE::JSONSchema
as W.Bumiller suggest.