core: Adding an existing block Storage Domain should be blocked

Adding an existing Storage Domain should be blocked by a CDA message

Change-Id: Iba5194e4c87ba96a7482fa52b18a2e9812663c7e
Bug-Url: https://bugzilla.redhat.com/1148803
Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>
core: Add lock when importing an exsiting block Storage Domain

Add memory lock while importing an existing block Storage Domain.

Change-Id: I43dfed013fcbf9965466a00e01b5c81cc6dc9174
Bug-Url: https://bugzilla.redhat.com/1148803
Signed-off-by: Maor Lipchuk <mlipchuk@redhat.com>