CA-125187: VBD allowed_operations fix

VBD allowed_operations checks should ignore running VDI.copy operations.
This wasn't needed before as VDIs weren't marked with the copy
operation.

Signed-off-by: John Else <john.else@citrix.com>
CA-125187: Don't automatically dismiss VDI operations during copy

We still want to allow VDI.snapshot while a VDI is being copied, as
well as multiple parallel copies.

Signed-off-by: John Else <john.else@citrix.com>
CA-126097: Block clone of live VDIs

Signed-off-by: John Else <john.else@citrix.com>
Fix test case name

Signed-off-by: John Else <john.else@citrix.com>
test VDIs should default to not sharable

Signed-off-by: John Else <john.else@citrix.com>
Improve readability of VDI allowed_operations test failures

Signed-off-by: John Else <john.else@citrix.com>
Add a case to a unit test

Signed-off-by: John Else <john.else@citrix.com>
Test that concurrent copies are allowed

Signed-off-by: John Else <john.else@citrix.com>
Add tests for clone/snapshot of VDIs during copying

Signed-off-by: John Else <john.else@citrix.com>
Add a test for VBD.allowed_operations

Test that a VBD.plug is not blocked by the VDI.copy which triggered it.

Signed-off-by: John Else <john.else@citrix.com>
CA-125187: Add explanation of the new behaviour

Signed-off-by: John Else <john.else@citrix.com>